Select 1 Fiend-Type monster from your Graveyard. Remove from play monsters on your side of the field whose total Levels exactly equal the Level of the selected Fiend-Type monster. Then Special Summon the selected monster from your Graveyard.
Rulings
Individual Card FAQs
Removing monsters on your side of the field from play is not a cost, so the opponent must decide if they want to chain before you select which monsters are to be removed. If they chain a card that negates the effect of "The Puppet Magic of Dark Ruler" you do not remove any monsters.
Face-down monsters may be removed from your side of the field.