Where limits have been announced, the playmat is restricted to one per transaction and the Curators Collection to two
The term "First Edition" refers to the early print run of these cards, which were marked with a small "1st Edition" stamp on the left side of the card
For example, if there are two +1/+1 counters on Aerith Gainsborough and it gets three -1/-1 counters, you'll put two +1/+1 counters on each legendary creature you control when Aerith Gainsborough's third ability resolves
This is how Infect, Amulet Bloom, and Twin approach the Burn matchup (not to mention decks like Storm, Griselbrand, and Affinity)
Of course, it has to die to do that, which means your opponents have to choose if its worth sacrificing their creatures, being slowly pinged to death, or just biting the bullet and hoping theyre not your target