You must choose two legal targets in order to cast Aether Helix. If there are either no permanent cards in your graveyard or no permanents on the battlefield, you cannot begin to cast it.
16-04-2021
wotc
If only one target is still legal as Aether Helix tries to resolve, it will still resolve and perform the appropriate action on the remaining target.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.