Power Bomberman is amazing the work you've done, it's the game that has more loved in this genre.
I think that before making new game modes, you should do something more simple, like making new stadiums, may at some future these will put them in new game modes, and there are interesting proposals.
We must appreciate that Jaklub you have done too much, and I would not want you to be very depressed by so many ideas that exists in this page.
I would help in any way, so I hope to take some objects into account:
Bomberman World (Arcade)
Should be objects that give you 3 bombs, or 3 flames.
https://www.youtube.com/watch?v=eHZbiroAeqw
Baku Bomberman 2 (N64)
The skull makes you almost always take a negative effect on the player, the demon object does give them a negative effect to all players.
https://www.youtube.com/watch?v=l2kgFgBGrPE
And as a final recommendation, players should only be cured if a skull grab an antidote, and not with any other object.
I hope not to have also bothered, and excuse my translation from Spanish to English.
Thank you.