Cards like Strategic Betrayal and Go Blank are strong not because they are inherently undercosted, but because they are different and if you play them in the right meta they will play more powerful than their mana cost
Abilities that define a creatures power and toughness apply while that card is in your graveyard, but abilities that add or subtract from it dont
Precon decks often have overpowered commanders to smooth over the jank often found in the 99 and this precon is no exception: Cloud, Ex-SOLDIER is incredible leading the stock list, immediately getting tremendous value the moment you cast him, providing card + mana advantage while beating face
This includes cards like the new Repurposing Bay, Simic commander Prime Speaker Vannifar, and a single-use sorcery version in Eldritch Evolution
Omniscience Omniscience is expensive at 10 mana, but once you get this card into play, the game is probably over