Theyre effectively counter-quadruplers, because both the initial replacement effect adding counters and the death trigger are enhanced
It's an open-ended question, but if you can't answer it everything else in the deck won't matter
I have yet to see someone open their fifth copy of a rare or mythic, though, so I dont know how much Vault progress those will give you
One important note before we move on, though: the amount of ramp in your deck and the amount of treasure generation can free you up for playing more enters-tapped lands, as this allows you to be more mana efficient
It won't trigger if you don't declare any creatures as attackers
The created card doesn't necessarily need to be from your deck, library, or sideboard, and could be a card in another set or format, as if it was created "out of thin air"