Anticlimax Boss: Amusingly, the final two bosses can both be taken down before the fight even begins, due to them both appearing on the map before the battle and still being damagable in this state. See here and here. The latter was fixed in the HD version, however.
Even without exploiting this, the fight with the Thug Leader on Snivelak can still be a joke with the Tankbot Glove. Simply head for a corner where the boss can't hit you, then maneuver tankbots in between its legs and mash the fire button until the tankbot explodes. Even with only 8 ammo, it's enough to do the job.
Demonic Spiders: The Y.E.T.I. on Planet Greblin. They are everywhere, highly durable, annoyingly cheap, and will do their best to prevent you from getting moonstones, often attacking in large groups. Some developers admitted they were coded in a rush and break some of the enemy guidelines they set, like short attack telegraphing and constantly attacking from behind. This actually got a Medal of Dishonor made for the studio, called the "Snowbeast Award", for whoever made the worst thing in a game made the previous year.
Designated Hero: Angela Cross. After The Reveal, she's treated as a misunderstood hero who's been thwarted by unsuspecting dupes. Though she was a Well-Intentioned Extremist, her crimes up to this point include kidnapping and holding Clank hostage, repeatedly trying to kill Ratchet, harassing store clerks for kicks, and generally just acting like an actual villain. Though we learn she was forced to resort to extreme measures to stop Fizzwidget from releasing the Protopet in its current state, her actions cross the line from extremism to villainy quite easily.
Even Better Sequel: Quite apart from Ratchet's improvement in professionalism and character, the weapons are more serious yet still creative, the number of worlds and gameplay elements increased, RPG-like elements such as the upgrade features were added, and the wrench controls became a lot less cumbersome. There's also a ton of new features and gadgetry, and even the Clank sections underwent some major changes.
The Bouncer can be this in all but the very last levels. It does massive damage on the initial blast and lets loose mini-bombs that seek out remaining targets and explode for additional damage. The final boss can be killed in a couple minutes just by bombarding it with Bouncer bombs.
The Plasma Coil is an okay weapon at first, hitting a primary target for decent damage and shocking nearby enemies when it hits. However, it upgrades into the Plasma Storm, which fires an orb of electricity that shoots out lightning at anything it passes. A single Plasma Storm shot is enough to clear entire rooms full of enemies. Better yet, its Challenge Mode forms upgrade its low initial ammo capacity of 15—the Mega form holds 25 shots and the Ultra form doubles that to a whopping 50! Finally, the fact that it's not affected by gravity and never needs to impact on anything to deal damage means it's great at handling those flying enemies the Bouncer tends to miss.
The Shield Charger is a magnificent example of Magikarp Power. It's initially weak and almost useless, it protects you from damage and does minor damage to enemies you touch. Stick with it though and it becomes the Tesla Barrier, which shoots lightning to zap any enemy that gets close to you, and it does good damage with it too. It noticeably helps against the Demonic Spider Y.E.T.I.
As last time, the RYNO II pretty much annihilates anything you aim it at. Yes, even the dreaded Y.E.T.I.
The Sheepinator makes fighting Protopets hilariously easy, killing them without using any ammo whatsoever (so you could save your ammo for the harder enemies of the level). The Black Sheepinator is even better, killing them faster and also turning them into sheep that explode.
The Spiderbot Glove, while usually ignored, can make some levels like Silver City on Boldan considerably easier. It is pretty strong and cheap for the point of game it is obtained (and later it can be strengthened further by Acid Mod) and it allows to engage enemies with Ratchet safely hiding behind corner or barricade, and enemies never think about destroying the drone. While holding only 8 ammo, the boxes restore generous 3 ammos, making it sustainable to be continually used. It then upgrades into Tankbot Glove, transforming it from mere guided explosive into Attack Drone, which while useless against airborne and scripted enemies, can engage everything else and especially can destroy one of more annoying bosses ridiculously easy.
Goddamned Bats: The Protopets. They keep reproducing if you don't get every single one of them and you often encounter them in groups.
Goddamned Boss: Megapede is not difficult to beat, but it has a large health bar, moves around the arena all the time, deploys irritating bombs en masse, and when whittled down by a powerful weapon, deploys mini-tanks with a difficult-to-avoid attack.
In first-person mode (the one you unlock after beating the game, not the "Hold L1" view), if you do a double jump and use the wrench, Ratchet will actually pop up a bit. If you are near a wall or ceiling, you can spam the wrench, allowing you to climb past obstacles and even skip Clank entirely if you so desire.
By using the above glitch, you can actually make it pretty far in the game without having to retrieve Clank* Up until Aranos, where there's an event flag to give you Clank again. If you make it to Joba and buy the Levitator, you can still use it... it's just that you don't have Clank, which hilariously leads to Ratchet magically levitating through the air.
Using the Charge Boots on Grelbin while being attacked by the Y.E.T.I.s can cause Ratchet to disappear with only his shoes, helmet and Clank being visible. In this state he is immune to damage, which means you can run around collecting Moonstones or beating Y.E.T.I.s at your pleasure.
Like in the previous game, you can clip through walls by using the Decoy Glove, allowing you to skip large portions of the game really easily.
Ho Yay: In the first cutscene, Ratchet is told he will learn a number of bizarre skills to become a commando, including ballroom dancing. Complete with an image of him in a fancy suit, dancing with a dress-clad Clank.
The Unknown Thief's true identity, being a female lombax-like species named Angela Cross. Of course, the series' "official wiki" does not care with the spoiler policy, so only a few fans would really not know about this before playing the game for the first time.
Captain Qwark is the Big Bad, and was impersonating Fizzwidget the entire game.
Porting Disaster: The HD remaster has some... issues. Glitching, the camera being obscured and the tour of the weapons facility having the audio removed, cutting the entire tour by half.
The physical Vita version apparently crashes whenever the player enters the Space Limo to travel to a moon in Maktar Nebula. The digital version doesn't have this problem, but both might crash upon beating the Mothership, which dies with a giant explosion.
Rescued from the Scrappy Heap: After the poor reception Ratchet received from the previous game, Insomniac Games replaced his obnoxious and self serving personality from the first game with the much more heroic and altruistic one that he would have for the rest of the series.
The prequel weapons available from the special vendor in the planet Barlow, which actually were very useful in that particular game, suffer a really bad case of the "Nerf Effect" / "So Last Season Syndrome" in this game and are generally next to useless when compared to your starting weapons as well as the later ones you'll eventually come across.
The Meteor Gun. While the previous gun you had (the Lava Gun) was an effective flamethrower weapon, this version merely turns into a slightly more powerful version of the Heavy Lancer with less effective range. The result is it loses its effectiveness against swarms of small foes and gets outclassed against anything else by the rest of your arsenal. At least you can purchase a lock-on mod for it, but this does not improve its effectiveness by much. In the weapon's appearance in Up Your Arsenal, it instead levels up into the Liquid Nitrogen Gun, which keeps the stream effect that the Lava Gun has.
The Zodiac. While a neat weapon in theory, the cons far outweigh the pros of it and its superannuated by more practical yet equally powerful weapons like the R.Y.N.O. II and the Bouncer. It costs 1,500,000 bolts (even more than the R.Y.N.O. II), it can only hold 4 ammo at any time (which is 10,000 bolts per shot and can't be replenished thru crates), only vaporizes whats on screen, and is useless against bosses. And to add insult to injury, you need to buy it to get the Weapon Envy skill point.
New Game+ has Clank Zapper. It costs as much as R.Y.N.O II, except is completely useless even when compared to prequel weapons and in fact, even non-Mega Tesla Barrier is probably stronger. The other issue is that there is no indication whether it's still active besides Clank's attacks, and when you'll get it for first time you'll probably waste a ton of ammo just trying to activate it because you won't realize it already is. The developers probably realized this too, because it is not needed even for 100% Completion.
The Scrappy: The New Age Mystic for being generally unhelpful and requiring the hard-to-get Moonstones just to do something.
While "Smash and Grab" on Oozla is feasible with the Wrench and Lancer, "Vandalize" on Maktar Nebula is a huge pain in the ass to beat without the Box Breaker (which can't be acquired until the midway point of the game). You have to destroy every breakable object in whats a fairly long level (save in the Jamming Array) and it is very easy to miss that one little hidden object or two you have to smash. "Destroy All Breakables" on Endako is equally frustrating for the same reasons.
The "Speed Demon" skill point on Barlow. You have to beat a Hoverbike race within a tight time limit of 2:10, meaning you have to spam boosts nonstop in order to make it. Challenge 3 makes it slightly easier due to the shortcut, but its still one of the toughest skill points to get. "How Fast Was That?" on Joba is also tough for similar reasons.
The "Wrench Ninja II: Massacre" skill point on Joba, which requires you to kill every enemy in the level with only your wrench and without dying a single time, is just as bad, as the enemies on that planet will often kill each other before you even reach them, and it's nigh impossible to hit some enemies without getting a few scars for your trouble. Fortunately, it's possible to come back after you get the second wrench upgrade, which allows you to kill the regular mooks in one Hyper-Strike, and the big purple mounts in two, and there will also be less enemies the second time around.
The "Dukes Up" on Dobbo's Moon against Thug Leader isn't really difficult, but extremely annoying. You have to destroy his mech only by melee attacks. Problem is, his mech is faster than Giant Clank and always runs away from you, so you'll have to wait when he flies up, uses missile or bomb attack, then flies back to ground, because he is immobile during landing phase, giving you opportunity to attack. This also means you'll be eating his attacks a lot, and while restoring health is easy by taking out Thug Choppers here, it means you'll have to break your pursuit to restore your health, making the fight even longer.
"Be A Moon Child", which requires you to collect every Moon Stone on Grelbin. While getting the Mapper on Damosel makes finding the crystals easy, getting to the crystals is anything but, due in part to the sheer number of Y.E.T.I.s. You will die a lot trying to get this one.
Swamp Monster II, an optional boss fight you can take up on Oozla once you get the Gravity Boots. It is a long and tough fight, due in part to its sheer resilience—there are no real shortcuts to bringing down this creature (although you can stall it momentarily with the Decoy Glove), and the lack of ammo crates in the area isn't helping your case. Do not fight this thing until you've built up a sizable and upgraded arsenal already. And to make matters worse, it is very easy to fall into the muck in the arena and sink, forcing you to start the whole battle over again if you aren't fast on your feet.
The third battle with the Thug Leader is tough for the reason of being a Marathon Boss. Normal weapons can barely even leave a dent, and you're forced to use the turrets all over the battlefield to even have a chance of damaging his mecha. However, you'll be spending more time shooting at some homing beacons, and every time 10% of the boss's health is taken, the turret will end up destroyed, forcing you to search for another one.
Boldan, for the abundance of heavily armed Thugs that can mow down your health in mere seconds if you let your guard down.
Snivelak probably takes the cake as the hardest level in the game, and its infamous boss fight doesn't help matters.
Grelbin. When you're hunting for crystals, Y.E.T.I.s will pop out from underground and they are TOUGH. They can survive at least one hit from any weapon you use (except the RYNO II), and will take a "bigger than average" percentage of your health if they swipe you. And how about those ice serpents that hide under frozen water, then burst out, take forever to kill, can knock you out quickly and can destroy your Shield Charger in one attack? And if you don't knock out those Y.E.T.I.s, they will chase you as long as possible.
Collecting the moonstones on Grelbin, as they're hard to find and protected by Y.E.T.I.s and Arctic Leviathans. The crystal-gathering sidequest on Tabora had similar problems, but at least the enemies there were manageable. Downplayed, though, as the Mapper shows where the moonstones are, making it much less of a trek to find them.
The Ace Bunyan space races, especially if you're going for the Platinum Bolt. You need to A) Collect every single ring, which have confusing hitboxes, and B) Still win the race. Fortunately, there's only 3 of these races in the game.
The PlayStation Vita port accidentally makes them even harder, as the Vita has a much more sensitive analog stick, although setting camera speed to slow seems to ease it up a bit. (Unless it's just placebo.)
The Ghost Ship challenge on Gorn. The aforementioned ship is extremely durable—you ship can barely put a dent in it, even when its fully upgraded—even the Nuke barely does any damage to it. Making matters worse is that its cannons hit hard and are very accurate, the ship can turn invisible for long periods of time to keep you from damaging it, and its slow movement constantly forces you to bank and turn, potentially robbing you of precious time to attack it when it becomes visible. And to add insult to injury, its flanked by a squadron of Thug starships to distract you.
Underused Game Mechanic: One of the 3 new robots that can assist Clank is the Lifterbot, which can lift up blocks for Clank. Or rather, it can lift up ONE block for Clank, and then never be used again.
Woobie Species: The one-eyed robots seemingly can't catch a break. They get blown up in a commercial and eaten by mutant squirrels on Todano, killed by security robots on Aranos, and massacred on their home planet, Damosel. Two skill points involve keeping them alive despite the hordes of enemies waiting to get them.