This is just a little idea I had. I have no clue whether it's been thought of before, or how many times, but I'll just throw it out there. =)
The goal of this mode is to have the "bounty" by the end of the time limit. The bounty is received by KO'ing the player that has it. At the beginning of the match, an "bounty icon" appears somewhere on the field, and whoever get's the icon first is the player you must attack. Once that player gets KO'ed, the player that KO'ed him get's the bounty, and thus becomes the player you must attack. If a character carrying the bounty is not KO'ed by another player's attack, but rather by a stage hazard or a personal mistake (falls off ledge), then the bounty icon will appear on a random part of the stage again.
So it would progress like this....
P1: Bowser P2: Pokemon Trainer P3: Donkey Kong P4: Ice Climbers
Bowser gets the icon. The target is now Bowser.
Donkey Kong KO's Bowser. The target is now Donkey Kong.
Donkey Kong is KO'ed by a roaming Bob-omb. The icon reappears.
Ice Climbers get the icon. The target is the Ice Climbers.
Ice Climbers get KO'ed by Pokemon Trainer. Pokemon Trainer is the target.
Time Out. Pokemon Trainer wins.
What do you think? =)