"Viral Attack"
I suggested this before but I think it's so frickin' cool: you give enemy pieces a nano infection. Infected pieces have a single-digit timer grafted onto their shell somewhere, counting down turns. In (for example) four turns, that piece will die and spread an infectious cloud of nanobots to surrounding pieces on its side, at which point those pieces now have the timer and four rounds to live.
These pieces also get a self-destruct button they can use at any time, which kills the piece early but prevents the infectious cloud.
Of course, purify would heal this.

