Hidetsugu and Kairi + Oracle of Tragedy
There is a gameplay bug that allows two cards to work together in a way that is not intended, giving too much card draw and free casts.
Opponent Spalteeple
Relevant cards:
Hidetsugu and Kairi
Oracle of Tragedy
Deadly Derision
Tidal Terror
The strangest interaction happened between Oracle of Tragedy and Hidetsugu in draft.
My opponent resolves Hidetsugu's ability, putting two cards back. (He puts Tidal Kraken on top.)
During my turn, I attack. My opponent blocks with Hidetsugu and the Oracle of Tragedy. They each die, triggering. Oracle's trigger on the bottom of the stack, Hidetsugu on top.
Hidetsugu's resolves, revealing Tidal Kraken. I lose 6 life. Oracle's ability resolves and shuffles back 3 cards, including Hidetsugu.
THIS IS WHERE THING WENT WRONG.
During the resolution of the Oracle's abilities, my opponent reveals two cards - Deadly Derision and Hidetsugu - and proceeds to CAST BOTH OF THEM WITHOUT PAYING THEIR MANA COST.
Somehow, the abilities being on the stack at the same time must've lead to some weird interactions.