What happens to the card or cards that were under the evolution creature?
Any cards under the removed evolution creature stay in the battle zone. The creature that’s now on top of the pile reappears in the battle zone. It’s tapped if the evolution creature was tapped, and it’s untapped if the evolution creature was untapped. It doesn’t have summoning sickness. If it has an ability that starts “When you put this creature into the battle zone,” that ability doesn’t work.