Ascended Meme: Enter a code at the pause screen to change ALL OF THE MUSIC IN THE GAME to Guile's theme.note Pause the game, hold Jump, and press Up, Down, Down, Down. A_Rival even titled the track "Goes With Everything."
Attack Reflector: Mega Man acquires one in the Aegis Reflector when he defeats Urien. Rose utilizes one in the form of her Soul Reflect. An enemy in Urien's stage also has this power.
Battle in the Rain: The landscape for the final battle against M. Bison is the Australia stage from Street Fighter Alpha 2, which contains heavy rain and thunder in the background. In version 2, if you see extra rain in the foreground, it means you have successfully met the conditions to fight Sagat.
Beating a Dead Player: Bosses will continue to run around and attack even after Mega Man has been defeated.
Blood Knight: All the Street Fighters. Why are they attacking Mega Man? Just because they can, but also because they want to fight him before their own anniversary finishes up and they don't want him to relax just yet for his own.
Boring but Practical: A skilled player can defeat any boss in the game with charged shots from the Mega Buster. Note the word "skilled": although charge shots will do a lot of damage compared to the normal Mega Buster shots or non-weakness weapons, the bosses still present a formidable challenge.
Bootstrapped Theme: Averted; while the usual Street Fighter suspects show up, they're used as they were intended: for the stages. Chiptune artist A_Rival even went a step further and mashed up famous Street Fighter themes with Mega Man themes.
The boss fights use "Volcanic Rim", the theme of Street Fighter IV — which has become something of a Bootstrapped Theme for the Street Fighter series as a whole in recent times.
Boss Rush: You'll go through one of these the third of the ending stages, as per Mega Man tradition. You can get health and ammo pickups by shooting at the balls in the Feng Shui Engine sitting in the main teleporter room.
Butt Monkey: On the traditional Acquired Weapon screen, Mega Man tests his new abilities on Dan.
Calling Your Attacks: Though since the game mimics the NES titles, it just sounds like bleeps. Particularly noticeable against Chun Li.
Doppelgänger Attack: Holding down Attack and Jump during the start screen for 6 seconds or so allows Mega Man to use Sei'ei Enbu (one of Yang's Super Arts), which creates a clone silhouette that attacks with him.
Dynamic Entry: Mega Man gets Hadouken'd by Ryu in the trailer — right at the end of the intro from Mega Man 2, no less.
Easter Egg: Several. It's possible to make Mega Man helmetless note at the Stage Select screen, place the cursor over Ryu, hold Shoot, and press Right, Right, Right, Left; simply repeat the process to regain Mega Man's helmet, change all of the music to Guile's Theme note at the pause screen, press Up, Down, Down, Down while holding the Jump button, and even obtain the Sei'ei Enbu and an alternate version of the Hadouken fired exactly like the real deal. note hold down both Shoot and Jump at the title screen for about 5-6 seconds; you'll hear a chime if you did it correctly
Elemental Rock-Paper-Scissors: Ryu > Chun-Li > C. Viper > Dhalsim > Blanka > Rose > Rolento > Urien > Ryu. Chun-Li > Vega (Claw), C. Viper > M. Bison (Dictator), Urien > Akuma.
Fake Difficulty: The game features a number of sections that pull this off. Enemies will respawn the moment they go off-screen (meaning they can still attack you), you can get locked into going down a hallway filled with one projectile spamming enemy and two enemies that reflect your shots, bosses have mountains of HP...
In the original release, there was no save function or password system, forcing you to play through the entire game in one sitting. Now, there is a password system in V2.
Flawless Victory: You can do this to bosses, and the screen will show "PERFECT!" when you do. Bosses can do this to you as well. You need at least four Perfects on the first 8 bosses to fight Akuma at the end, and in Version 2 you need 4 of them on the Shadaloo bosses and the rematches in the Boss Rush stage to fight Sagat.
Note: You don't necessarily have to not get hit to get the "PERFECT!" Just have full energy at the end of the match. You can E-Tank it up and land that last hit to get it.
Hoist by His Own Petard: Ryu's weakness is his own Hadoukens reflected back at him (the same applies for Akuma, but with his Shakunetsu Hadoukens instead). Balrog's Violent Buffalo eventually sends him into a pit.
Asexpected, Ryu's Tatsumaki Senpuukyaku makes an appearance here as well. While it provides Ryu with invulnerability, Mega Man can also slide underneath it.
Likewise, Chun-Li has her Spinning Bird Kick, which Mega Man can also slide under.
Iaijutsu Practitioner: One of the mooks in Ryu's stage. You have a very small timeframe where you can actually hit it.
Improbable Weapon User: A number of Blanka's attacks use watermelons as weapons; this serves as a nod to his Tropical Hazard super in Street Fighter Alpha 3. Mega Man gains the Tropical Hazard after beating Blanka, which gives him the ability to spawn watermelons to use as either a weapon or a temporary springboard for a super-jump.
Rose counts, as she infuses her stole with Soul Power to mold it into a versatile and surprisingly deadly weapon.
Innocently Insensitive: The match with Balrog can carry some odd implications to a crafty player. The boss is unharmable to Megaman's weapons. He can, however, be slowed down. Since Tropical Hazard is affected by gravity and slows down to hit behing Megaman as he runs, this makes the best weapon againt Balrog to be... watermelons.
Kaizo Trap: One of the game's extremely rare energy tanks is found at the end of Balrog'sAdvancing Boss of Doom, but you only have a split second to nab it before the victory animation takes control of Mega Man. At that point, it's far too late to kill yourself to restart the level, and you can't go back for it once the next stage starts.
Kamehame Hadoken: Ryu has this in the form of his Shinkuu Hadouken, though in this game, he uses the usual ball ofki instead of the energy beam associated with Vs. series). Mega Man obtains the Hadouken after defeating him, and he can charge it up into the Shinkuu Hadouken.
By holding down Attack and Jump at the start screen for about 6 seconds, you can let Mega Man learn this early (do the quarter circle forward motion and attack). He even charges it up just like Ryu if you do this.
Limit Break: Staying true to the spirit of Street Fighter, all of the bosses have their own Super Meter that fills up as they incur damage (similar to the Revenge Gauge in IV). Once the meter fills up, the bosses can unleash Super Combos. Getting killed by the super even results in the signature Yellow and Orange starburst background. Defeating a boss with the Sei'ei Enbu active also nets you one.
No Fair Cheating: Using a cheating device such as Cheat Engine will turn the screen black. You can't undo this without restarting the game.
One-Hit Kill: Balrog's punches, as well as Akuma's Shun Goku Satsu, definitely fall under this trope.
Only Six Faces: Many of the Street Fighters have their character model based on Mega Man's.
Painfully Slow Projectile: Ryu's Hadouken and his Metsu Hadouken are extremely slow. His Shakunetsu Hadouken is not, however. Dhalsim's Yoga Catastrophe is also extremely slow, if not slower than Ryu's Metsu Hadouken.
And of course, Dan's Ultra Combo, Shinkuu Gadouken, makes an appearance when you get the Aegis Reflector.
Power Copying: Hey, Capcom couldn't call it a Mega Man game without this trope.
Psycho Electric Eel: One of the Mooks in Blanka's stage looks like these, a likely nod to Blanka's origins (he was taught how to harness his bio-electricity as a weapon by watching eels).
Respawning Enemies: Taken Up to Eleven in Chun-Li's stage, where the Metool cars and Pandas keep coming in from offscreen endlessly. You can take advantage of this to get lives, though.
Retraux: Much like Mega Man 9 and Mega Man 10, SFxMM homages the 8-bit presentation of the earlier Mega Man titles. Unlike those two games, however, SFxMM merely mimics the look, as numerous sprites surpass the limits of NES graphics.
Reverse Shrapnel: Rose's Soul Satellite from SSFIV makes an appearance here. When she uses the Ultra, she summons two spheres of Soul Power that orbit around her body and deal collision damage. Mega Man gets this move when he defeats her.
Rubber Man: Another staple ability of Dhalsim's makes an appearance here.
Rule of Cool/Rule of Fun: Why are Mega Man and the Street Fighters at war? How is Mega Man's Weapon Copy compatible with humans? Where did all the robot mooks come from? Why would the Blood Knight-inclined Street Fighter cast hide behind a bunch of robotic mooks in the first place? Why can Mega Man fire his weapon at humans? These are all valid questions which very likely have a sound and solid reason behind... y'know what? Just shut up and play the game.
The Tropical Hazard weapon is pretty much the Mega Ball from Mega Man 8, except it sticks to gravity.
The panda enemies in Chun-Li's stage are based off Yun and Yang, right down to their clothing and their way of skating. note For a possible added layer, in SSFIV: Arcade Edition Chun-Li knows the twins on a personal level and could even be considered their martial arts elder sister.
Rolento's pogo makes the same sound as Scrooge's in Capcom's DuckTales.
The flower enemies in Blanka's stage are obvious ones of the flower enemies in Solar Man's stage.
Bison's stage is a twofold one. It's a stormy grassland in Australia, a direct recreation of the backdrop for the Ryu vs. Sagat opener of Street Fighter II: The Animated Movie and the stage it inspired in Street Fighter Alpha 2, but could also be seen as a nod to Bison's stage in Alpha 3, which had a similar atmosphere (despite being set in Thailand instead).
Another layer is added if you fight Sagat in version 2, as the stage was actually his own to begin with.
Spikes of Doom: Compared to other Mega Man games, SFxMM goes light on this one. Bonus points for Blanka's stage using Bamboo punji pits instead of the traditional spikes.
Sword Beam: There's an enemy in Ryu's stage that fires these out.
Tarot Motifs: Rose's stage has enemies based off the Minor Arcana (coins, swords, cups), as well as "The Fool" card as a physical barrier numerous times in the stage. Given that Rose is a fortune teller, this is very apropos.
Training Dummy: Just like he is in Street Fighter IV, Dan is the training dummy that Mega Man practices his newly acquired moves on. He even does his Super Rolling Taunt as his introduction.
True Final Boss/Bonus Boss: If you get a Perfect on 4 of the first 8 World Warriors (the Boss Rush does not count), Akuma will challenge you by interrupting your fight with Bison, killing him with Misogi as "HERE COMES A NEW CHALLENGER!" flashes on the screen.
In version 2, if you get 4 Perfects in the Shadaloo stages, including the Boss Rush, Sagat will challenge you before the final battle with Bison. This is indicated by additional rain effects when you enter Bison's stage.
Updated Re-release: Street Fighter X Mega Man v.2 which fixes some bugs, buffs M. Bison, adds a password system similar to the one in Mega Man 2 and adds a brand-new boss: Sagat.
What Could Have Been: Yang was considered as one of the bosses, but was replaced by Chun-Li. His supposed boss weapon, Sei'ei Enbu, is still in the game via a code. One of the enemies in Chun-Li's level bears some resemblence to him and his brother Yun.
The creator wanted to include alternate costumes for the bosses as well as a second playable character, though the second one would be from the Street Fighter franchise.