Ok let's say I play the card {sleep}. My opponent had 5 creatures, 2 tapped and 3 untapped. {Sleep} taps all creatures and THOSE creatures don't untap. My question is, since as far as I know you cannot tap an already tapped creature, do the creatures that were already tapped prior to {sleep} being played stay tapped? It's a little confusing lol so lemme know if u need some clarification
If sometging is tapped and you use {Sleep} then it would not untap.
The ruling is stated strangely, but it actually does have 2 abilities. 1st is tap all creatures opponent controls, 2nd says those creatures don't untap, meaning opponents creatures.
All creatures that player controls when Sleep resolves wont untap on their next upkeep, it doesn't matter it Sleep caused them to tap or if they were already tapped.
If they 'gain' a creature, it'll untap. If one of the creatures untaps and re-taps before that upkeep, it wont untap. Say they use mana to untap a {Galvanic Alchemist} and tap it for {Stern Mentor}'s ability, it would not untap.