Spirit Warrior is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

How it works : Spirit Warrior

Original English text — Wizards of the Coast / Scryfall

No additional ruling has been published for this card.

Interactions with other cards

These cards' text mentions Spirit Warrior.

Ascendant Spirit

{S}{S}: This creature becomes a Spirit Warrior with base power and toughness 2/3. {S}{S}{S}: If this creature is a Warrior, put a flying counter on it and it becomes a Spirit Warrior Angel with base power and toughness 4/4. {S}{S}{S}{S}: If this creature is an Angel, put two +1/+1 counters on it and it gains "Whenever this creature deals combat damage to a player, draw a card."

Figure of Destiny

{R/W}: This creature becomes a Kithkin Spirit with base power and toughness 2/2. {R/W}{R/W}{R/W}: If this creature is a Spirit, it becomes a Kithkin Spirit Warrior with base power and toughness 4/4. {R/W}{R/W}{R/W}{R/W}{R/W}{R/W}: If this creature is a Warrior, it becomes a Kithkin Spirit Warrior Avatar with base power and toughness 8/8, flying, and first strike.

Kin-Tree Invocation

Create an X/X black and green Spirit Warrior creature token, where X is the greatest toughness among creatures you control.

Warden of the First Tree

{1}{W/B}: This creature becomes a Human Warrior with base power and toughness 3/3. {2}{W/B}{W/B}: If this creature is a Warrior, it becomes a Human Spirit Warrior with trample and lifelink. {3}{W/B}{W/B}{W/B}: If this creature is a Spirit, put five +1/+1 counters on it.