I know which heartless it is, Its the bulky vendor. It's the one that looks like a gumball machine.
If you mean that randomly appearing heartless that gives you items if you catch it, then sorry, no. Why do you think this enemy is strong? That surely isn't the sephiroth of the heartless.

The problem is, you're thinking of the wrong type of heartless.

Uuuuuh, that was a hint!

Stilll 6 more guesses