The decks they give out for free are good, but the grind towards building anything beyond those few decks seems to be frustratingly slow, especially when compared with a similar competing game like Master Duel
2 Archon Of Cruelty From Modern Horizons 2 comes the incredibly powerful Archon of Cruelty
If it has no loyalty counters on it, it will be put into its owner's graveyard
Cephalid Coliseum (Ext, S, Block) While not usable before threshold is achieved, and quite painful until then, the Coliseum provides a quick and easy way to filter your hand
Zethi, Arcane Blademaster If you look on the EDHREC page for Zethi, a lot of the instants listed are already pretty efficient, but I think it makes more sense to add more expensive and impactful instants instead of copying Opt or Curate