Whenever you cast your second spell each turn, put a +1/+1 counter on this creature.
Thunder Drake’s ability can trigger only once each turn. The ability will resolve before the second spell resolves. It doesn’t matter if the first spell you cast that turn has resolved, was countered, or is still on the stack.
Thunder Drake must be on the battlefield in order for the ability to function. Notably, the ability won’t trigger if Thunder Drake is the second spell you cast in a turn.
