Okay, so I was browsing the posts when I came across an ice related post, so I had some ideas.
Icy-bot (Sword bot)
Whenever it hits something it freezes the area around the sword. This area will be permanently frozen, and the ice will slowly eat at the frozen voxels, one at a time.
Shock-bot (Archer bot)
The shock-bot's arrows will stun anything for a short period of time, but won't destroy voxels.
(I know people have come up with similar ideas, I'm just expanding a bit.)