Millennium Seeker — Ruling

Effetto 1

This card's effect that Special Summons it is a Trigger Effect that can be activated in the hand. (It can be activated during the Damage Step.)

This card's effect that Special Summons a monster from your opponent's Graveyard to your field is an Ignition Effect that can be activated on the field. (This effect targets 1 monster in your opponent's Graveyard. You cannot target a monster with "?" ATK.)
When resolving this effect, your opponent can choose 1 monster from their Deck. (They cannot choose a monster with "?" ATK.) If your opponent does not choose any monster, Special Summon the targeted monster to your field.
When your opponent chooses a monster, the ATK of that monster and the ATK of the targeted monster are compared. If the targeted monster's ATK is higher, Special Summon it to your field and return the opponent's chosen monster to the Deck. If their ATK is the same or if the targeted monster's ATK is lower, your opponent adds their chosen monster to their hand.