wizards of the coast mtg cards Original Spin

They mutate into the creature on top plus all abilities from under it.)\nFlying, first strike\nWhenever this creature mutates, you may cast target noncreature card with mana value 3 or less from your graveyard without paying its mana cost.

Valgavoth, Harrower of Souls

This Bloomburrow Family Matters Commander Deck includes 1 deck of 100 Magic cards (3 Traditional Foil cards, 97 nonfoil cards), a 2-card Collector Booster Sample Pack (contains 1 Traditional Foil or nonfoil alt-border card of rarity Rare or higher and 1 Traditional Foil Uncommon card), 10 double-sided tokens, 1 deck box (can hold 100 sleeved cards), 1 Life Wheel, 1 strategy insert, and 1 reference card

How do you know the right number of lands