Skyla from BreakPOINT can be found for a reasonable price, and I suspect her inclusion in the new Shiny Fates set will push all of her cards up in value in the short term
The First Doctor also allows players to planeswalk, which can only be done in the Planechase format of Magic: The Gathering
Metalworker Metalworker can generate lots of mana in an artifact deck, which you can then use to cast some of the artifacts that you reveal from your hand
You can Shock the same target, the next one doesn't include the word "another"
Prowess Prowess had previously appeared as the Jeskai Clan mechanic in Khans of Tarkir and Fate Reforged , though it played out smoothly enough to earn temporary evergreen status with Magic Origins, though it was later demoted to deciduous, which meant it would be used sparingly without being locked to any set or plane's flavor
You can only activate 1 "Herald of the Abyss" per turn