Flash - Advent Drifting Spirit (Either Attack Step)
By sending Soul Core to your Trash, stack this from your hand onto your target spirit.
[LV1][LV2][LV3] (When Summoned/Advents) You can move one core from an opposing Spirit to another opposing Spirit.
[LV2][LV3] (When Destroyed by the Opponent) You can summon one Spirit card among this Spirit's pre-Advent cards, without paying the cost. When you've done so, return this Spirit to your hand.