Gameplay scenario thoughts

Swords as keys
Fast swordplay---button mashing is fine, reward people for being careful and precise, same button for blocks and strikes combined with directions for specific abilities, maybe an extra button for something special
Charge up sword for attacks---Gem coming in contact with the sword's allow causes the metal to superheat
Also ultimate charge-up mode---cut through everything?
Steal energy: No resource management, but maybe one character can do it/in all other cases it's unseen
Athos: Gun has knock-back effect
Porthos: Gun is like firework/missile launcher that knocks people into air
Aramis: smoke/stun so he can dance around with gun--blinds enemies
Dart: Grapnel that goes point-to-point to connect cut off parts
Stuff is reattached to set points, dependent on ability
Attached parts work according to dynamic rule set that makes sense for each thing

Mechs power down as they take damage, and auto-repair when they are charged up again.
Recharge with single-person sword combat


To support cooperative/camaraderie:
Special pick-ups only one player can get
Shared store---nobody upgrading by themselves
No random strangers in games---only organized play