Karn's Temporal Sundering, reveal it due to Kefnet's ability, making a copy that costs ({2} magic symbol) less to cast.
Cast the copy for ({2} magic symbol) ({U} magic symbol) ({U} magic symbol) , granting you an extra turn and returning up to one nonland permanent to its owner's hand.
Results
Infinite turns.
Metadata
This combo produces a lock.
In 172 decks according to EDHREC.
Bracket Tag
This combo has been estimated to be Ruthless (Bracket 4+).