Just make sure the Cube includes enough support
Most Atraxa decks focus on the Poison mechanic, but thats far from all she can do
Stonecloaker For 2W, you can exile a card at instant speed in response to something, and then be ready to do it again if you so desire

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5 Blood Moon The red enchantment Blood Moon sees ample play in competitive formats like Modern, where it shuts down greedy manabases, and it's just as effective in Commander, where dual lands, tri-lands, and utility lands are often used
#7: Force of Negation This inclusion to the list at first can look like a bit of an eyebrow-raiser, but I think this card serves a valuable purpose if the Modern Horizons gives birth to degenerate Turn 2 or Turn 3 combo decks in the Modern format