You could place bonus gems in the level anyway. You could also add a coin warps to a regenerating (maybe even blue) gem in a sucker tube or the scoring area/base.

Another random thought:
Applying more than 1 damage to a player at once -> steal one of his gems (if he has any). Or steal one gem on normal damage and 2 gems on higher damage. Just to keep the gems moving while no-one dies for a while.



Yes, this sounds good. Somewhat like Team Treasure Hunt.