Uro and Oko
I was 2-0 after 2 first matches, match 3 was 1-1 and i was in the lead in game 3.
I had Mandrills in play, Oko in hand, opponent was hellbent and casts oko from from graveyard. In my tur i resolve Oko, and elk the uro, no block. Turn after opponent attack oko with Uro like I expected, but here is the bug: The Uro aka Elk triggers on attack oppent draws and gain life. Draws new creature, and the game runs away for him, my loosing my potential 3 of 5 matches.