Is smash chopped liver? And whatever vs capcom as well?
A game is not defined just by their characters and settings, but by their mechanics, so if you were to take let’s say a hulk video game, there has to be mechanics to crush the environment, toss things around, enemies that can get scared of you, bosses strong enough to do the same to you, and then put him into the black widow video game, metal gear solid but with less nave gazing and more beating an opponent 3 power level clases above you by ingenuity and sneakiness, what kind of game you get when you put one in the other game?
Black widow jumping around in a city frail enough that she can punch buildings off? A bunch of diconnected stages that bring nothing to the crossover? Her just being sneaky in a long city level where she doesn’t has the power set to get the fun of?
And that is not imagining what happens with hulk in an air vent, either killing everyone including captured civilians on the underground base in a rampage, or making just enough noise that even the dumbest of bosses decides to escape before confronting Hulk.
Fighting games and musou games give the flexibility for a character to bring their own mechanics in, creating gameplay instead of gacha games or puzzle games, but providing a base framework where they can coexist.
Things like marvel whatever that plays like a diablo like where you collect heroes, manage to work because there is not a strong cohesion between the base games of each individual character and the whole, just take Spider-Man only working as a combatant , not sneaking around swinging across cities, it would be a bad use of resources to create New York just to have people like Wolverine forced to slowly climb, or nick fury using the elevator or a cab to get where they have to be.
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If it is the same gameplay.. odyn sphere does it in one game.
Metal gear and dmc tried to push forward the younger hero and wasn’t as well received.
Pikmin 3 has all the captains.
The other thing is that movies are a low investment of time by the part of the audience, captain America will be over in less than 2 hours and I’ll be able to understand everything about it from there on forward. What happens to those who like solid snake but don’t like raiden or big boss, and just go from mgs1 to 4?
Something else that becomes obvious with combining series, like in jump force, protagonist are bad at following orders, and them doing what they are told is just out of their character, so you’d have to mold the story in a way that lets them (or you) decide how to proceed. Naruto eventually becomes the hokage and it is part of a military unit, and Luffy is a pirate captain TV at would know how to lead, but would not lead if he didn’t feel like it, but who thought that it was a good idea to put Goku in charge of anything is beyond me.