Card

Kindred Discovery

Mana cost {3}{U}{U}

As this enchantment enters, choose a creature type. Whenever a creature you control of the chosen type enters or attacks, draw a card.

Part of 41 known combos, 3 of them two-card. 4 official rulings.

Bracket

B1 Exhibition — Not in the same deck as its two-card combo partners: Cryptcaller Chariot, The Locust God, The Watcher in the Water
B2 Core — Not in the same deck as its two-card combo partners: Cryptcaller Chariot, The Locust God, The Watcher in the Water
B3 Upgraded — Not in the same deck as its early two-card combo partners: Cryptcaller Chariot, The Locust God, The Watcher in the Water
B4 Optimized — allowed: No restriction beyond the banned list
B5 cEDH — allowed: No restriction beyond the banned list

Two-card combo with Cryptcaller Chariot, The Locust God, The Watcher in the Water (early with Cryptcaller Chariot, The Locust God, The Watcher in the Water)

Bracket: Lotus Vault analysis, with Commander Spellbook flags

41 known combos, 3 of them two-card.

Cryptcaller Chariot + Kindred Discovery
Produces: Infinite self-discard triggers, Near-infinite creature ETB, Infinite draw triggers
View on Commander Spellbook
The Locust God + Kindred Discovery
Produces: Infinite card draw, Near-infinite creature tokens with haste, Near-infinite creature ETB
View on Commander Spellbook
The Watcher in the Water + Kindred Discovery
Produces: Infinite card draw, Infinite draw triggers, Near-infinite creature tokens
View on Commander Spellbook

2023-09-01 · Wizards of the Coast
You can't choose multiple creature types, such as "Cat Warrior." A Cat Warrior is both a Cat and a Warrior. It's affected by anything that affects either type and unaffected by things that affect non-Cat or non-Warrior creatures.
2022-06-10 · Wizards of the Coast
You must choose an existing creature type, such as Human or Warrior. Card types such as artifact and supertypes such as legendary can't be chosen.
2022-06-10 · Wizards of the Coast
The choice of creature type is made as Kindred Discovery enters the battlefield. Players can't take any actions between the time the choice is made and the time it enters the battlefield. Notably, this means that if it is entering the battlefield at the same time as any creatures of the chosen type, its last ability will trigger.
2017-08-25 · Wizards of the Coast
If you somehow control a Kindred Discovery with no chosen creature type, its last ability can't trigger, even if a creature with no creature types enters the battlefield or attacks.

Rulings: Scryfall · Wizards of the Coast