After playing with it a few times, the free copy you get for the first artifact, instant, or sorcery you cast provides so much impact on the board, especially with some of the newer cards provided later in the year like Portal to Phyrexia, Flow of Knowledge or Cosmic Epiphany
You can only use each effect of "Predaplanning" once per turn
With Master Duel being best-of-one, this makes Numeron even better when compared to a TCG duel
Costing one mana of each color, with the Black mana being Phyrexian, Omnath is a 4/4 with two powerful abilities The cards first effect causes unspent mana to become Black
This is particularly true for foil cards, as the plastic layer on the front does not swell as much as the paper backing
Brawl also has its own relatively short list of banned cards, but since this is automatically enforced by the Arena client theres no danger of accidentally building an illegal deck