(BUG) Tasha, Unholy Archmage +1 last longer than until your next turn
In a direct game, on PC my oponent used the +1 on Tasha, making attacking creaturs get -1 counters till that players next turn. They passed the turn, i killed Tasha on my turn, and passed back.
When it was my turn again I attacked with all my creatures and they got -1/-1 counters. but the effect should gone away after my first turn where i killed Tasha.
In the second game my opponent had her out for 3 turns ticking her up every time. on that occasion they stacked so that when i finally attacked there was 3 -1/-1 counter triggers

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Rides1 Klepto#23515 commented
As you can see in the attached screenshots, my opponent had four instances of Tasha's +1 ability stacked up, I attacked an they went away, but my attacking creature got four -1/-1 counters.
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bambibandit#21181 commented
I just had this happen to me playing Tasha, I think its bugged. My opponent didn't attack Tasha or myself one turn and attacked a second plainswalker so Tasha's -1/-1 counters didn't trigger. However when it passed to my turn the ability didn't go away, despite the ability stating "Until your next turn" and it proceeded to stack with the +1 from that turn.
I managed to do it again the next couple turns as the opponent didn't attack and it allowed the Tasha +1s to stack over the 2 turns.
Attached is a log from the game (I think) I had detailed logs enabled so if this isn't the correct one I would be glad to find the correct one. However a ctrl+f found the player name of my opponent in the file so I think it is correct.