The ability to counter two spells just shuts down any deck not heavily based on winning with creatures (which includes many combo decks as well as control however getting this into play and active before a combo deck kills you can be a challenge)
Arena Directs increased from a 5,000-gem entry fee to 6,000 with Tarkir: Dragonstorm , and it was noted at the time that events for Universes Beyond products would increase that cap to 8,000 gems
Runaway Steam-Kin is great on turn-two and works great with Experimental Frenzy, but its very weak to removal and can be a bad draw later in the game
Do they require an overly specific build
Teferi, Master of Time Let's turn to our only planeswalker
Valgavoth, Terror Eater Cruel and vast, the demon Valgavoth has an insatiable appetite for fear