Many of Muhammad Ali's insults towards Michael Jordan are in the same vain of the insults he used in real life to taunt upcoming opponents. He would call them ugly, claim that they were sell-outs to white people ("Uncle Tom" is the term Ali used towards numerous fighters in his career), tell them they look more like a creature than a person, etc. In the battle, he even uses the term "whoop" (as in "I'll whoop you"), and he doesn't use it the way the current generation tends to (usually saying "I'll whoop your ass"), because that's not how he used it in real life.
Additionally, after his conversion to Islam, calling Muhammad Ali "Cassius" (or "Clay") was an easy way to get him pissed off. After Jordan actually DOES refer to him as "Cassius," Ali's tone becomes more aggressive and he even threatens to "leave [Jordan] flat on [his] ass."
Sherlock Holmes' first verse begins with his deduction that Batman is Bruce Wayne. Almost no one in the DC Comics world knows this, yet Holmes was able to figure it out immediately. How was he able to do so? He's a master sleuth who can make connections between entities that almost no one else may have even considered.
Most rappers have a distinct style that fits the character that the public knows them as (Mr. Rogers talks softly and gently, Mr. T yells a lot, Skrillex uses the "stutter" technique that's popular in dubstep during his vocals, etc.). Two things that stand out to me are Sherlock Holmes and Shakespeare's raps. They both make very good use of multis (multisyllabic rhymes— i.e., "Deuce stain," "Bruce Wayne." The two phrases rhyme, as opposed to just one word rhyming with another), and they rhyme on the same line impressively ("No gonads, egads, it's so sad"). This could be because Sherlock Holmes is always portrayed as an amazingly quick thinker who can formulate brilliance in almost no time at all, and Shakespeare because, obviously, he's a literary genius. Their rhymes seem to stand out from the other rappers', most of whom use basic rhymes, and sometimes words that don't rhyme at all.
In the Dr. Seuss vs. William Shakespeare rap battle of Epic Rap Battles of History, I noticed that many other fans claimed that Shakespeare's first verse didn't flow well. But then I remembered the lyric "I hath gone iambic on that ass, ye bastard" and gave it a second listen. Shakespeare's first verse is actually in iambic pentameter and once you realize that, the first verse flows perfectly with the beat. - Kaxbe
During Einstein vs. Hawking, Stephen Hawking sings "I've got 12-inch rims on my chair, that's how I roll y'all". It turns out that really is how Stephen Hawking rolls.
Or it just means he prefers Dark Helmet (the character, and Vader's parody) over Vader himself.
"Little known fact, also dope on the mic" - Not just about the rap battle thing, but referencing how Hitler motivated Germany with his reknowned speeches.
The reason Captain Kirk hates Columbus so much is because Columbus is one of the greatest examples in history of why the Prime Directive is necessary.
Also why Kirk's rap derails towards the end into an attack on Queen Isabella.
Columbus's claims he has 'a neck chop for Spock, I'll put my sword through Sulu' aren't threats, they're boasts - Spock is famous for his 'Vulcan neck pinch' and Sulu is a fencer.
When Elvis tells Michael Jackson that he has a rap for his monkey, it might refer to Bubbles... or, given Jackson's status among many, it might refer to his other monkey.
When the Cat in the Hat raps about Macbeth, the blackboard behind him has the equation "1+2=SO MUCH BLOOD". Later, Things 1 and 2 show up and start threatening to stick their feet up Shakespeare's ass.
The reason why Dr. Seuss never spoke himself and let his creations rap for him? The real Dr. Seuss died from cancer in his jaw/throat area, which made it very difficult to speak in the days before he died.
Also why Vader claims he's the one who invented everything that Hitler did.
Hitler tells Vader that he appears to be in pain, right after the latter removes his iconic helmet.
He also tells Vader to take a trip on his train. The obvious joke is a reference to the transportation of Jews to concentration camps, but it also references one of the several ways his opposition tried to assassinate him; where they bombed the train Hitler was supposed to be on.
I always thought Hitler could've won the rematch if he'd stopped with his "Sieg fucking heil!" line. Of course, he is known for going too far...
Lincoln did win the Civil War "Four Score and Sixty-Five years in the past". Lincoln Vs Chuck Norris was released in 2010 and was exactly 145 years since the Civil War ended in 1865.
How come in the Mario Bros. VS Wright Bros. battle, Luigi is the Ax-CrazyLarge Ham? It could be part of his Mr. L personality showing through, partially summoned by his anger towards the Wright Brothers.
Or it could be because Luigi has previously had to fight a dude named Orville.
It's because the Marios are doing the Public Enemy bit, with Luigi playing the role of Flava Flav. Notice his bling is about the size of an alarm clock.
And why are 8-bit fists more badass than quarters? Because quarters are only 2 bits.
Why does John Lennon hate Bill O'Reilly so much? Well Lennon was a leftwing activist. If he was alive today, he would hate O'Reilly and his ilk.
Hitler refers to Vader as "black". This is not only a reference to his armor's color, but also to the fact that he is voiced by James Earl Jones.
Not necessarily brilliant, but there's something darkly hilarious about a old white guy with a Southern accent telling a black dude to get the fuck out of his neighborhood.
The HAL 9000 going up against Bill Gates makes sense when you remember that HAL was a potshot at IBM.
Beethoven's comment "Ask Bach, I got more cock than Smith & Wesson" seems inexplicable when you know that Bach died twenty years before Beethoven was born. Then you realize Beethoven is probably not talking about THE Bach (that would be Johann Sebastian) but one of J.S.'s equally musical sons, Wilhelm Friedemann and Carl Philipp Emanuel. Epic Lloyd (who portrays Bach in the Beethoven vs. Justin Bieber rap) even looks a bit like C.P.E Bach.
At the end of the Doc Brown vs. Doctor Who rap, the announcer proclaims, "Who won? Who's next?" as he always does. Then the Doctor comes back to start the rap over and finish it early, thereby winning the battle. Who, indeed.
Shakespeare's Sophisticated as Hell style makes a lot more sense when you realize how many dirty jokes he put in his plays.
Doc Brown tells the Doctor to not bother trying to out-rhyme him. If you check their lines, you'll see that the majority of the Doctor's lines in either incarnation don't actually rhyme, while Doc Brown had at most one Painful Rhyme (which was the rather excusable Hot-Watts).
Out of eleven Doctors to choose from, they chose the Tenth and Fourth. These Doctors have been considered to be the most iconic and received great acclaim from fans.
Obama vs. Romney is unique in that it was right before an election, and had the power to influence voters. The implications of a one-sided battle would have been enormous, and an indicator of ERB's political leanings. The candidates' bickering and Lincoln's intervention do a crucial job of keeping things balanced.
Why is Clint Eastwood so racist towards Bruce Lee? It's a reference to his character in Gran Torino.
Clint Eastwood was playing dirty. Fitting, as Clint Eastwood (the actor) also played Dirty Harry.
"You can't have children" is probably the most devastating insult Cleopatra could come up with. Not for emotional reasons, but because Cleopatra, as an ancient queen from a long dynasty, would have heard all her life that having children was the only way to ensure her family's continued rule. And unlike, say, Catherine of Aragon, she was successful here, having three sons and a daughter. (Granted, one of her sons was murdered and the other two disappeared from the historical record, and this after she died and her kingdom was absorbed by Rome.)
In Michael Jackson VS Elvis Presley, during Jackson's second verse, Elvis begins eating sandwiches. He is first shown just casually taking a bite of one like it's a lunch break, but then after Jackson's line "Then you made one daughter, she came to me", he starts wolfing them down faster and looking enraged. He got his Berserk Button pressed by that line and tried to get his anger out by eating while waiting for his second verse, and in that time ended up gaining a lot more weight, hence his transition into "fat Elvis".
The inclusion of someone named Steve in the Adam vs. Eve fight makes no sense until you remember one of the anti-same-sex marriage arguments was "Adam and Eve, not Adam and Steve".
In Adam VS Eve, Adam gets the line "When things are good they're great and it's like I'm dreamin', until your junk starts bleeding and you turn to a demon!" This has actually two different meanings; the first is the obvious reference to females becoming crankier when on their period; "turn to a demon" as in turning into a demon. However, in the traditional Adam and Eve tale, Eve was the one who first accepted the forbidden fruit from Satan; hence the second, more subtle "turn to a demon" as in turning and listening to a demon or devil.
The beat to Gandhi vs Martin Luther King Jr. ended with a gunshot. Both men were shot and killed by assassins.
Gandhi's comment about staying away from the hoes seems out of place, but Dr. King was known for having a number of emotional trysts. This actually caused him a lot of guilt, which means what looks like an inexplicable opportunity for an awful pun is actually a surgical strike on King's self-confidence.
It's a double-whammy: He said it applies to protests as well. Hoes in protests? Not so much. But hose (as in fire hoses being used to disrupt protests)...
Doc Brown's opening Catch Phrase, "Great Scott!" has double-meaning here — David Tennant, the actor who played the 10th Doctor (the one of the first verse) was Scottish.
Babe Ruth rips into Lance Armstrong pretty bad for his admission of cheating, but he also makes a reference to calling his shots- there's been a strong debate over whether or not Babe Ruth was cheating by instructing pitchers to throw specific pitches. In "The Babe" he makes several enthusiastic points into the air as if he's eager to hit a home run, while actual footage of that very same event from the original game shows him merely making a hand gesture to someone- exactly where has been largely debated. Though despite the debate, no actual proof of Ruth cheating ever came to light and the general agreement was that the shot was not called in the manner of cheating, but rather he simply pointed his intent to hit a home run as a taunt to the Cubs and then hit the home run.
First, Mozart makes the crack, "I'm a prodigy, sonny, and I'm about to smack a bitch up!". Prodigy's most famous song is "Smack My Bitch Up", and Skrillex's first name is Sonny. Then he says that Skrillex "reeks of dead mouse", a pun on Skrillex's friend/rival Deadmau5.
Skrillex's line "I'm a rock star, mix you with the bass and drop ya!" seems pretty straightforward; he's making a pun on "drop the bass", saying he'll mix Mozart with said bass so he can drop Mozart while he drops the bass. However, "mixing" in music terminology is when you put a song together and add effects to it so it sounds good. So Skrillex is also making a subtle pun on the term "mixing".
The Skrillex side of the instrumental has segments that sound like various actual Skrillex songs, whereas the Mozart segments shift over to a more classical music sound.
Mozart refers to Skrillex's music as "skrill-excrement". Considering Mozart's apparent documented of feces-related humor throughout his life(of which Skrillex insults him for in the prior verse), this crack makes even more sense than being a one-off pun. He does it AGAIN in his next verse when he refers to a part of a Skrillex song as "the 68th measure of diarrhea".
In his verse, Stalin yells "Shot!" four times. Exactly as many times as Rasputin was shot when assassinated.
"If your name end with '-in', time to get out." Not just a potshot at the three standing there or foreshadowing Putin, but a bonus jab at Boris Yeltsin.
The real reason Freddie Mercury got on his feet was Frank Sinatra implying that he was using his bisexuality for publicity ("You'll do anything to get famous!")
It's also a roundabout jab at Sinatra himself, who's rumored to have such a background, as well as being resentful of the rise of rock taking away some of his fame. Mercury, in contrast, was out most of his adult life, even when it was more taboo in the 80s, which makes Mercury's rebuttal all the stronger.
In the season 2 finale, each rapper only gets a single turn. However, if you pay attention Nice Peter and Epic Lloyd do alternate turns the entire time, keeping with the usual (if modified) formula.
Why do Santa's elves love bacon so much? It's a great way to keep warm at the North Pole.
The beats in the Season 2 Finale start of grim, then happy, then triumphant. Why? The beats reflect Russia's history. Rasputin's and Stalin's are dark because in their times, Russia wasn't a great place to live in. Rasputin was manipulating the king and millions were starving. Then under Stalin's time, millions of people were dying in camps or getting shot, Poles were being massacred and the Germans were attacking Russia. In Lenin's time, the people were starving and killing off the Tsars and starting a revolution. However, by Gorbachev's turn, where the beat gets very cheerful, Russia was slowly opening its arms to the West and things were improving. When the wall was torn down, Russia was happy for the first time in years. And if you're wondering why Putin's beat is triumphant and uplifting, it's because by the time he was in power, Russia was truly happy and no one was starving anymore.
Why is Lenin so angry at Rasputin and Stalin? The peasantry of Rasputin's times blamed him for using his position with the Tsarina, making a corrupt regime worse, and before Lenin's death he had specifically stated he didn't want Stalin to succeed him. After Lenin's death, Stalin went so far as to doctor photos to "prove" Lenin favored him.
"Who built a superpower, but he paid the price!" Possibly, in addition to its obvious meaning, a subtle call forward to when Rasputin says "If you're the Man of Steel, I spit kryptonite!"; both are Superman references. The first by bringing up superpowers, the second with "Man of Steel".
Stalin's name literally means "steel" — he chose it for just that reason.
Notice how Stalin is having difficulty with That Russian Squat Dance during the Epic Dance Battle at the end? That's because he's not really Russian. He's actually from Georgia. All the others are from Russia proper:
Rasputin was born in Siberia
Lenin was born up the Volga from Moscow
Gorbachev was born in Stavropol, which is south of Moscow
Putin was born in St. Petersburg
Beethoven's remark about Justin Bieber being a "Little White Usher" actually has a double meaning. The obvious meaning is what is shown in the video, where Bieber turns into a ticket usher; but it also refers to the fact that Usher is the name of a musician who helped promote him.
At first, Beethovens inclusion in the season 2 trailer seems misleading, but then you remember that the Mozart Vs Skrillex battle had a similar premise to the Beethoven Vs Justin Bieber battle: Classical musician Vs modern musician.
In Master Chief VS Leonidas, how did Master Chief get out of the pit? Simple: he had the Jetpack.
Also in Master Chief VS Leonidas, Leonidas chides the Chief, saying "I've had better battles with my six-year-old son!" John (the Chief) was taken from his parents when he was six years old, and it was then that he began his forced training and transformation into the Master Chief we know today. Sure, doesn't really work its way into the dis, but it's still a nice little tidbit they slipped in.
Gandhi's suggestion that MLK plagiarize from him seems a bit odd at first. However, MLK did commit plagiarism in college, which Gandhi was mocking him for.
Why did Gandhi reject MLK Jr's forgiveness at the end? Because despite Gandhi being a pacifist spreading peace and love, he was borderline racist against black people. See here and herealso herethis one too.
One of Gandhi's lines is "Leave your thoughts on the door, like the real Martin Luther." Martin Luther was also the name of the 16th century founder of the Protestantism (a division of Christianity) who hammered his thoughts on a church door in Germany.
Boba Fett is only on screen for a short while, barely getting to say anything, but leaving an impact before being unceremoniously killed off. This sounds about right.
Why does Rasputin keep dancing during Putin's verse? Because Putin mentioned "schooling every communist сука" and Rasputin isn't a communist, so it doesn't offend him.
Why is Lady Gaga played by NicePeter? Because, as Sarah Palin alludes to, when she first debuted, many people thought she was actually a transvestite.
In Vader vs Hitler 2, Darth Vader raps the line "Ask Indiana Jones who the fuck I am". Before this, I always thought because the only reason this line was there because Han Solo and Indiana Jones are both played by Harrison Ford. However, The Indiana Jones movies (or at least the original trilogy) take place in the 1930's, and the Nazis are recurring enemies in the movies. Hell, Indy bumped into Hitler at one point in The Last Crusade. So Hitler had the chance to ask this to Indy in person!
Hitler makes the Incredibly Lame Pun of "A War on Two Fronts" to start off the third rematch. This actually becomes a very clever foreshadowing of the end when you realize that was precisely what led to everything crashing down on him toward the end of World War II.
Blackbeard starts by trying to distinguish pirate stereotype from the reality. Later one Al Capone makes a bunch of remarks about him having a bunch of crumbs stuck in his beard. This is obviously a case of Shown Their Work in realizing that the life of an actual pirate was really quite horrific due to the terrible living conditions of any sailing ship at the time (though pirates would have it especially bad since they'd have to spend the most time at sea). Among other things, most sailors would have very bad hygiene (or in Blackbeard's case, plenty of stuff caught in his extremely thick beard) because they were unable to wash themselves due to a need to conserve their supply of drinkable water.
Al Capone comments how he's been 'slapping bitch-ass teaches back since I was 14.' Makes more sense when you remember Blackbeard's real name was Edward Teach.
When Putin says he's "a President in [his] prime", it works in two ways: when he first became president, he was in his 40s, which is relatively young for a democratically-elected leader to hit the head of state; also, he served as the prime minister of Russia, both before his rise to the presidency, and from 2008 to 2012 (while there are no hard term limits on the presidency in Russia, no president may serve more than two consecutive terms).
When Pablo Picasso is switching channels on the television, it shows clips of previous battles. In addition to the channel number being the number of that battle, every character who appears on it (Billy Mays, Mr. Rogers, the Fourth Doctor, and Bob Ross) are famous for being on television - Billy Mays for his commercials and everyone else for their own television shows.
Bob Ross's remark about "dropping bombs like this is Guernica" makes sense when you realize that Guernica was an actual painting by Picasso, which he was inspired to make in response to the innocent people killed during an actual aerial bombing that happened during the Spanish Civil War.
The line "You fight like the little girls who made your Nike shoes." becomes a much stronger diss after you realize it's coming from a professional boxer.
Something similar to the Season 2 finale music changes happens in the Donald Trump vs. Ebenezer Scrooge battle. Initially, Trump's beat starts slowly, as Marley took a while to convince Scrooge he was there. After that, Scrooge's beat initially starts out chilly, the high-pitched spikes calling snowfall to mind. The beat gets moving during J.P. Morgan's verse,representing the beginning of Scrooge's road to redemption.Scrooge's second verse retains the chilly atmosphere of his first, but parts of Morgan's theme are still found, meaning that altough Scrooge says he wasn't affected, he was shaken slightly.The sudden change starting from Kanye West represents that, in the book, Christmas Present deals Scrooge a few blows that begin to shatter his perception of Christmas as a "humbug". It is kept in Scrooge's third verse, representing the fact that, after the encounter with Christmas Present, Scrooge is truly shaken.Yet to Come changes the beat ever so slightly, as he really drove the point in and made Scrooge understand.Scrooge finally changes his ways in the fourth verse, and the same beat is kept.
Longtime fans may have noticed some deliberate censoring in at least two tracks, "Wright Brothers vs the Mario Brothers" and "Donald Trump vs Ebenezer Scrooge". That's because the nod to Super Mario Bros. and A Christmas Carol may draw the attention of younger viewers, unlike say, Rasputin vs Stalin or Blackbeard vs Al Capone.
In Donald Trump VS Ebenezer Scrooge, notice how J.P. Morgan appears as soon as the clock in the background strikes one, and the Ghost of Christmas Yet to Come begins his verse (with "Boo!") as soon as the clock chimes a third time (you have to listen really carefully to notice it chime more than once). However, Kanye appears a second or two after the clock chimes a second time. In the original A Christmas Carol, the Ghost of Christmas Present (whom Kanye replaces here) appears a little bit after the clock strikes two.
Why does Scrooge refer to "the Dead Donald's lecture" when Donald Trump is still alive and there was no indication of him dying in the battle? Donald Trump's role in this battle was to inform Scrooge that there are problems with his lifestyle and that he shall be visited by three ghosts who will help him change. In A Christmas Carol, this role was played by the ghost of Jacob Marley, who had died shortly before the beginning. This is even alluded to when Donald Trump displays a briefcase chained to his arms over his back, similar to how Marley is often depicted being heavily bound in chains with money boxes and various items associated with his life and warns Scrooge that a similar fate awaits him if he doesn't change.
In Vader vs. Hitler 3, Vader asked Hitler if Napoleon didn't tell him to pack some winter clothes when he invaded Russia. This might seem straight enough, but on a much earlier battle (Napoelon Dynamite vs. Napoleon Bonaparte), Dynamite subtly insults Bonaparte for being one of the things that has failed in Russia, which refers to Bonaparte's failed invasion to Russia. This adds three layers of brilliance:
Layer one, a Napoleon did indeed say something about Russia, albeit implicitly.
Layer two, that Napoleon told it to the other Napoleon, so in a sense, Napoleon never told Hitler anything about the whole stuff.
Layer three, Napoleon Dynamite and Napoleon Bonaparte are played by Peter and Lloyd respectively, who also plays Vader and Hitler. So, in a sense, Napoleon did tell Hitler (or perhaps, Vader himself told Hitler).
Knowing about the Holodomor puts Stalin's line about starving Rasputin until he wastes away into an even uglier light.
"Anyone who sold you pierogi, shot!" Pierogis are a common dish in Poland, and well... 
Stalin refers to himself as "the man who made Mother Russia his bitch". Fair enough, "Mother Russia" is a common nickname for the country, and he certainly ruled it with an iron fist. But more studious viewers might know that "Mother Russia" can also be used to refer to an Anthropomorphic Personification of Russia, much like Britannia is for Britain. And considering this isStalin talking, one wonders what horrors he might be referring to...
In both of his appearances, Abe Lincoln takes pot-shots at the Republican party. Odd, considering that he was a republican and his main opponents (and the people he fought in the Civil War) were primarily Democrats.
The rap was a time loop until he ended. Subsequently it is kinda hard to sort out past from future, so he could have regenerated into a past incarnation instead of a future one easily enough. Also, regeneration is a random process. No rule he can't have the same face twice, or even one we'd never seen before..
Fridge Brilliance: It is implied in Day of the Doctor that eventually, the Doctor will regenerate back into Tom Baker and take on the role of the Curator, as he was revisiting some of his previous incarnations, but "just a few old favorites". With this in mind, it's perfectly possible that he revisited David Tennant's incarnation, and the regeneration seen in ERB is his regeneration into the Curator.
Why does Lenin claim that Stalin was "supposed to be his right-hand-man" when he specifically did not want Stalin to succeed him and saw Trotsky as his second?
It may have been intended as a Take That towards Stalin's efforts to rewrite history by claiming he was Lenin's right-hand man. His next line immediately points out that for Lenin's supposed right-hand man Stalin did absolutely nothing to respect his memory.
How does Wilbur Wright pull his dress shirt off when it's both buttoned and under a pair of suspenders?