I think a bomb defuse minigame would be really fun.
It would announce that a bomb is about to go off in the chat (maybe have little bomb out of the text) and viewers would have to type !cut (wire color, 4 colors seems like a good number). The color required to cut would of course be randomized. When someone cuts the correct wire, it will announce that <winner> has successfully defused the bomb and saved the chat, (maybe configurable messages) and it'd give them a reward. If they lose and cut the wrong wire, it'll announce that <loser> cut the wrong wire and the bomb went off etc.
A possible fun configurable thing for cutting the wrong wire is the bot can purge the last 3-5 chatters so it look like a bomb went off in chat.