MTG Combo: Krark-Clan Ironworks + Myr Retriever
Infinite ETB & Creature Death:
Requires: Two Myr Retrievers
Sacrifice Myr Retriever #1 to Krark-Clan Ironworks
Cast Myr Retriever #2
Sacrifice Myr retriever #2 to Krark-Clan Ironworks
Return Myr Retriever #1 to your hand with Myr Retriever #2's death trigger
Loop.