New thought for a mechanic. Probably worded horrendously, but how fun do people think it would be?

The bit about dealing its damage even if it's removed from combat is very odd. I've seen "Last strike" proposed a few times, as a minor drawback; Wizards even tried it with Goblin Flotilla, Mammoth Harness and Spitting Slug. But the idea's always been that it can be stopped from dealing damage by killing it first. Otherwise, what difference does it make?

The idea being that it gets its licks in whether or not it dies. Like Tangle Asp, but less hideous.

In which case, may I suggest making it a 0/3 with "Whenever ~ blocks or becomes blocked by a creature, ~ deals 3 damage to that creature at end of combat"?

But if it's not around at end of combat it can't be a source of damage, surely? And also adding last-strike to a creature then wouldn't have a meaning. I guess it could be templated laststrike:x (where x is usually what the creatures power should be/was)

The ability as I phrased will go on the stack at end of combat even if this thing's disappeared; Last Known Information will be used for the damage it deals. It's actually happened once before: Sawtooth Ogre.

I can see that it doesn't make it grantable in the same way. You could instead have "Whenever this creature blocks or becomes blocked by a creature, prevent all combat damage it would deal this turn, and at end of combat this creature deals damage equal to its power to that creature". That's phrased in terms that could be reminder text for a keyword ability.

"Last strike" is a really confusing name for something so different (not just opposite) to first strike, though.