When the lines between gaming realities blur, when story lines don’t make sense and when publishers want easy money, it results in the ‘crossover’ effect.
These are the the Top 7 Ultimate Gaming Crossovers caused by this effect!

7. Battletoads & Double Dragon

Battletoads created by Rare, Double Dragon the classic brawler created by Technos. Combined together they create kick ass brawling mayhem.

How they could come up with this crossover is a bit of a mystery, no doubt it probably spawned from an erratic staff meeting…

CEO: “The Battletoads sales are slipping!”
CEO: “We need to find a way to boast their sales!”
Employee: “Lets combine them with Double Dragon!”
CEO: “Done! CA-CHINK!”

And thus it was born.

The gameplay isn’t bad, it doesn’t bring anything new to the table but if you are looking to mindlessly beat up some thugs for less then an hour then this game is for you.

(Chock full of witty banter)

6. Super Robot Wars Series

Big O, Escaflowne, Eureka Seven, Evangelion, Full Metal Panic, Getter Robo, Gunbusters ,Gundam, Macross,  Mazinger Z,  Nadesico, RahXephon, Tekkaman and that’s only scratching the surface of the crossover mayhem.

I was a bit indecisive about including this in the list since the proper games haven’t really been released in the west, but with the pure awesomeness that is bundled in the games I just couldn’t ignore it.

Any mecha who is worth his weight is included in this series, although unfortunately due to the nightmare of licensing the games for the English market only the ‘Original Generations’ games have been released (but that doesn’t stop fan translations).

The gamplay is RPG style and the battles are turned based, as you progress through the game you can recruit all the good mechas & pilots to team up with you to battle the villains from the various shows who for some reason or another have formed an alliance of evil.

5. Capcom vs. SNK 2

Bringing together the best fighters from Capcom and the best fighters from SNK is any old school arcade jocks’ wet dream.

Capcom primarily used their characters from the Street Fighters series, but characters turned up to represent Rival Schools, DarkStalkers and the Final Fight series.
SNK characters were from mainly Art of Fighting and Fatal Fury, but a few turned up from King of Fighters and Samurai Showdown.

Compared to CvS1, CvS2 is leaps and bounds better then the original, 6 different grooves to fight with, lots more characters and combos which don’t feel cheap.

4. Diddy Kong Racing 64

Nintendo’s Donkey Kong, Rare’s Conker and Banjo plus an assortment of new characters come together to compete in the ultimate showdown against the evil lord Wizpig by racing planes, boats and carts to beat him.

Rare didn’t just create Diddy Kong Racing to be an awesome racing game, they also created it to introduce two new rare characters who would both spawn their own franchises Banjo and Conker.

Although the crossovers is minimal the game play is so great it easily makes up for it, the gameplay is similar to Mariokart except it also contains hover craft racing and plane racing.

3. Marvel Vs. Capcom 2

I’ll probably be viciously attacked by Capcom Vs. SNK fans for ranking this above it, but in my opionion it’s a hell of a lot of fun, even if button mashing is the winning combination.

There is a massive 56 playable characters, 28 from Marvel and 28 from Capcom. Including from Capcom Megaman, Morrigan, Strider and nearly the entire Street fighter gang, and from Marvel… most of the X-Men, Iron Man, Captain America, Sentinel and many more.

This is by far the biggest crossover brawler released in the west, and fortunately for casual gamers its mechanic have been heavily simplified for pick up and play, although the infinite combos do get a touch annoying.

2. Kingdom Hearts 1 + 2

Fighting Cloud and Sephiroth with Donald Duck and Goofy on your team surely sounds like some twisted Fanfic from the mind of a child, but indeed it does happen in all its awesomeness.

Kingdom Hearts is summed up as Disney meets Square, although predominantly Disney based most of the main characters from the Final Fantasy series do make appearances.

Why is it number 2, although it’s lacking on the cross over front it has great gameplay, a fun storyline , it’s great to see the characters from different Final Fantasies finally interacting with each other and it is packed full of nostalgia.

Squall and Cloud!?

1. Super Smash Bros. Brawl

The showdown we all argued about as kids, the fight we thought would NEVER happen, it’s finally here! Sonic versus Mario!

SSBB brings together one of the most varied crossovers in a fighting game, including Snake from Metal Gear, Ike from Fire Emblem, Ness from EarthBround, Samus from Metroid, nearly every famous Nintendo character and of course Sonic from Sega.

SSBB is full of fanboys dream battles, being able to pummel Pikachu and Mario with Snake is such a life fulfilling experience.

Gameplay is basically a party brawler, mash the buttons as fast as possible and hope to win.

Why it’s the best? Characters we never thought would come together have, battles we never though could happen happened, it’s an insane crossover game that deserve its place as number 1 on this list.

Upcoming

Mortal Kombat vs. DC Universe

How the Mortal Kombat crew are going to stand up against Superman is going to be interesting, but no doubt it’ll make for a fun game.

Official Site

Misc
The list only includes games with a release in English and with crossovers between two or more companies.
Pictures taken from official sites & wikipedia.