WotC unbanned five cards: Gifts Ungiven, Sway of the Stars, Braids, Cabal Minion, Coalition Victory, and Panoptic Mirror
Toxic is a creature mechanic that deals combat damage to a player in two ways: in life based on the creature's power, and N poison counters based on the creature's toxic N attribute
That's a bit of a departure from how energy was originally used in the Kaladesh sets, where it wasn't tied to any super-thematic strategies
[Copy Editors Note: Hey, I resemble that remark!] One of my first control decks, named The Masterpiece by Michael Flores, was a four-color monstrosity that solely generated card advantage from this enchantment
Plus, the ability to cast all creatures, not just the ones on top of your library, with any mana you have laying around is a great gift for decks with a bunch of colors, like the four-color Commanders printed just last year