Typical examples are kicker, buyback, bargain, phrases like As an additional cost to cast this spell, sacrifice a creature, and commander tax
In the future, this is a bias I need to be more cognizant of
Then, I can tap this artifact at any time to put a creature on the battlefield if it has a mana value equal to the number of charge counters on Aether Vial
Bazaar of Baghdad (T1) Bazaar of Baghdad also seems to provide complete card disadvantage on the surface
Its actually not the most synergistic with Spirits in all cases, so the commander may matter, but with multiple Legendary creatures in the deck, I think this synergizing poorly with the main commander means its less likely to get reprinted but you still have chances for it to go in another deck
At just U, the Bottomless Pool side offers a cheap, reusable bounce effect that could provide some interesting tempo plays in limited