Corrupted Keys

Target 1 face-up Xyz Monster you control; Special Summon 3 "Umbral Horror Mirage Tokens" (Fiend-Type/DARK/Level 1/ATK ?/DEF 0). (When Summoned, each Token's ATK becomes equal to the that Xyz Monster's current ATK. They cannot attack your opponent directly or be Tributed, except for a Tribute Summon.) When that face-up Xyz Monster leaves the field, destroy these Tokens.