Figured it out! The creatures cannot gain any abilities throughout the game. Got it when I took all the auras out of my deck. I don't think that was how it was intended but here we are.

Just in case I didn't have 5 creatures the first time

Add me to the list of those not getting the achievement

You need to cast 5 creatures. I have done so and have still not received my achievement. Ridiculous.

Edit: TWICE I have fulfilled this, the second time without any adventure creatures. This is simply bugged.

just saying this task is so difficult because people literally scoop when they think they have lost. but since you have to play 5 vanilla creatures AND win the game it becomes one of the hardest tasks in the game

achievement says you need to cast 5 creatures with no abilities and win the game. however I can tell you I casted 5 creatures and it didn't complete. the creatures I casted were Tyrox, Grizzled outrider, quakestrider ceratops twice, and a twin vale treefolk. unless the other half of the card having an adventure doesn't count I should have gotten it.

You need to cast 5 creatures but it still doesn't work even when you do.

The achievement does not say you need to cast 5 creatures. If that is the intent then it needs to be reworded in game. I have also completed multiple games where Yargle is my only creature and have no received this achievement.

The achievement says you need to cast at least 5 creatures.