In the current format, its relatively easy to get cards into your discard
Gimmicky planeswalkers are ones that have a twist to them, only having negative abilities, maybe being an uncommon walker, a nonlegendary one, one centered around only zeroes, one that transforms, one that has a plus that can get it to an ult directly by adding loyalty counters, etc
How much milling efficiency would you give up for a shot at a zero-mana 9/9
Play boosters combine the high-value card experience of opening set booster packs while still being a viable product for drafting
Speaking of cheap cantrips, I've always sort of felt like Faithless Looting got a bit of a raw deal by being banned alongside Hogaak, Arisen Necropolis as its primary enabler