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During the combat phase, after I assign a blocker, can I then tap that blocker for its activated ability? What would happen? For example, say that a 1/1 Saproling token equipped with Healer's Headress is assigned to block an attacking 3/1 Blade of the Sixth Pride, but after it's assigned, the Saproling is tapped to prevent one damage to it. Is that legal? Would anything change if the attacking creature had first strike, like Ambush Party?