614.8. Regeneration is a destruction-replacement effect. The word “instead” doesn’t appear on the card but is implicit in the definition of regeneration. “Regenerate [permanent]” means “The next time [permanent] would be destroyed this turn, instead remove all damage marked on it and tap it. If it’s an attacking or blocking creature, remove it from combat.” Abilities that trigger from damage being dealt still trigger even if the permanent regenerates. See rule 701.12.
701.6b The only ways a permanent can be destroyed are as a result of an effect that uses the word “destroy” or as a result of the state-based actions that check for lethal damage (see rule 704.5g) or damage from a source with deathtouch (see rule 704.5h). If a permanent is put into its owner’s graveyard for any other reason, it hasn’t been “destroyed.”
Please autocard , check it on [read this first] - creating a rules thread.
I'll just throw a couple out to help myself make sense of this. She attacks with Blight Mamba and I block with Vampire Outcasts which would destroy the mamba. Then she would say wait, I want to regenerate it.Can she do that, or does she need to declare the regen prior to combat?