Arbor Elf You need a reason to play Arbor Elf over other 1-mana dorks like Llanowar Elves and Birds of Paradise
As long as you haven't yet chosen to do that this turn, all instances of sacrificing a creature will cause Riveteers Ascendancy's ability to trigger
C Common Hero Counterattack X TRAP When an "Elemental HERO" monster you control is destroyed by battle: Your opponent chooses and reveals 1 random card from your hand, then, if it is an "Elemental HERO" monster, you destroy 1 monster your opponent controls and Special Summon the chosen monster
Those formats werent so blisteringly fast that youd be left behind after taking turns one and two off
But Im not gonna spill the beans here if you want to learn more about this, check out the First Partner Packs page for it and other info about the release
Yap city, but it's my thoughts