Still looks like a more expensive Rain of Fire. But I really like the concept. Reminds me of Bombs from the Final Fantasy Series. Maybe increase the damage and decrease the health a bit?
Yes, HP should definitely be less. It's a freaking POT so it having 10 HP is pretty ridiculous. On the other hand I think if it's less than 5, it would be too easy of a target to Otyughs. I might drop it to 5.
increased damage? Hmm.. not 100% sure about that. Keep in mind that you play more than one at a time which would clear the whole table pretty fast.
I don't have strong feelings on what the actual effect is. It's all good. I just want to time bomb concept because it would bring an interesting new strategic element to gameplay when you have to wait for the bombs to explode before you can play your creatures, etc.