Opponent used disarming elemental to place a 6 cost mistress of mixtures on top. I played Theotar and swapped the mistress for a 2 cost Deliverance (opponent played renounce darkness). The Deliverance was showed to cost 2, but after the swap it cost 6.
The mistress was later played for 6 mana; I didn’t get to cast the deliverance.
TLDR: Theotar copied the cost of 1 modified card onto another modified card