Professor Onyx gives every instant or sorcery cast or copy a multiplayer drain effect. Each magecraft trigger makes every opponent lose two life and gains you two life. A black spellslinger deck can use ordinary draw spells and interaction to pressure the table while maintaining its own life total.
Chain of Smog provides a notable combo. By targeting yourself and repeatedly choosing to copy it, you can generate repeated magecraft triggers while Onyx remains present. The copy option does not require successfully discarding two cards each time, so an empty hand does not by itself stop that sequence. Opponents can still interact with the pieces or the stack.
Her loyalty abilities support a slower game as well. The plus ability selects one of the top three cards and puts the others into the graveyard, giving both hand selection and graveyard setup. The minus-three ability forces each opponent to sacrifice a creature with the greatest power among their creatures, which can remove large threats without targeting them.
Each magecraft trigger gains you two life total, even in a game with several opponents. The opposing losses are two per opponent. That distinction matters when budgeting life payments or calculating a recovery turn: the life you gain is not the sum of all life opponents lose.
Six mana makes Onyx a significant investment, especially when you want to cast another spell immediately. Ramp and cheap follow-up spells help secure value before opponents attack the planeswalker. You do not need to rely entirely on a dedicated combo: a steady sequence of spells can make the drain meaningful over time. Keep the deck's card flow and protection strong enough that the six-mana payoff has useful work to do after resolving.
