So far, I haven't seen anything tempting me to put it into my cube, and I won't add any traditional 3-color cards, but I really like the mechanics!
Connive is a loot variant, that actually adds power. Probably good for myself to be forced to actually win a game and not just accumulate value
Casualty could be interesting, especially on generally useful spells in black and red.
Blitz is another cool tool for aggro and sacrifice, if they manage to deliver some elegant but strong designs.
Alliance aka creaturefall is obviously good, works with tokens, blink etc., although it feels a bit "cheap" for a faction mechanic.
Shield counters smell like future evergreen maybe. I mean, ward does a good job of being a finally balanced shroud variant, but shields also seem like a nice way to give an expensive threat some staying power without making it impossible to interact with it.