Ability costs can include ink (paid by exerting cards in your inkwell), exerted cards (paid by, well, exerting cards) or something else explained on the card itself
weve even seen mechanics based on Cycling produce non-card effects (Ghost-Lit Warder, Hunting Triad)
Twinflame Tyrant is a new Dragon that costs just five mana for a 3/5 with flying, and if you deal damage to an opponent or something an opponent controls, that damage is doubled instead
With the amount of mana that Elves can generate, Helix Pinnacle can quickly close in on 100 counters, stopping any time you want, depending on how quickly you want to end the game
That makes combat way more explosive and punishes players who try to stay safe by not attacking
Even in other tribes, Kindred Summons isn't a bad finisher