The original design for Mtenda Lion, a one-mana green creature from Mirage, was a little more, shall we say, aggressive.
Bagnali Lion was a 2/1 for that could not block blue creatures and did no damage to blue creatures that blocked it. Not a bad color-affiliated drawback… but what blue deck played creatures in that era?! Blue was all about control and countering, meaning the Lion's drawback didn't even affect it in the relevant match-up! Okay, so it was bad against Merfolk, but that hardly makes up for the fact that it is a hyper-efficient weenie in every other situation.
To fix it, R&D created a blue-based drawback that would actually come up when playing against blue decks, and shipped the "can't block" clause over to another green common in the set, Gibbering Hyenas.
The fix worked; Mtenda Lion was hardly seen on the tournament scene.