Vigor

[Hakuu]

So with {Vigor} on the BF, I attack with a 3/3 and they block with a 4/4. Does my creature become a 7/7 and kill their creature, all DMG get prevented and my creature become 7/7 and theirs survives or something diff all together?

[Kagain123]

I'm assuming their creature doesn't have first or double strike. Since damage happens at the same time, theirs would live, and yours would be a 7/7 after damage would be dealt to it. If their creature had first strike, theirs would deal 4 damage, thus putting 4 +1/+1 counters on your creature, then yours would deal 7 damage to theirs, thus killing their creature.

[Hakuu]

No first strike, but infect

[Wackaman9001]

Infect alters what the damage does but vigor would still stop it. You would net a 7/7 and he would have gained nothing

[Hakuu]

So,just to be clear, in a non first struck situation both creatures survive and mine gets the counters.

[ChrisRodriguez]

So,just to be clear, in a non first struck situation both creatures survive and mine gets the counters.

Yes