How you answer these questions will vary based on your playstyle and deck, so dont be afraid to experiment until you find a blend of mana ramp cards that works for you
With access to enough colorless mana and a creature that generates mana on ETB, Displacer can set up easy infinite combos, one of which was even possible in its Standard format alongside Brood Monitor and Zulaport Cutthroat
As the EDH format allowed only one copy of any given card in a deck, the Highlander part of its original name was, of course, a fitting one
Many such cards like Entomb and Chrome Mox got their ticket to Arena through a Limited event, or Arena Anthology, or show up very infrequently like a Special Guest that earn a pre-ban so as to not shake up any pre-existing legality
The value racks up quickly with life loss triggers all over the place