Cannot be Normal Summoned if you control a monster. You can Tribute this card; Special Summon 1 Machine monster from your Deck whose ATK equals its own DEF, but return it to the hand during the End Phase. You can banish this card from your GY and discard 1 card; Special Summon 1 "Iron Rubble Token" (Machine/EARTH/Level 1/ATK 0/DEF 0), but it cannot be used as material for a Fusion, Synchro, or Link Summon. You can only use each effect of "Checkker" once per turn.