Card

Thought Reflection

Mana cost {4}{U}{U}{U}

If you would draw a card, draw two cards instead.

Part of 63 known combos, one of them two-card. 3 official rulings.

Bracket

B1 Exhibition — Not in the same deck as its two-card combo partner: Peer into the Abyss
B2 Core — Not in the same deck as its two-card combo partner: Peer into the Abyss
B3 Upgraded — allowed: Its two-card combos are not early, which Bracket 3 allows
B4 Optimized — allowed: No restriction beyond the banned list
B5 cEDH — allowed: No restriction beyond the banned list

Bracket: Lotus Vault analysis, with Commander Spellbook flags

63 known combos, one of them two-card.

2020-08-07 · Wizards of the Coast
If a spell or ability causes you to draw multiple cards, Thought Reflection's effect doubles each card draw. For example, if you cast Harmonize (“Draw three cards”), you'll draw six cards.
2020-08-07 · Wizards of the Coast
If two or more replacement effects would apply to a card-drawing event, the player who's drawing the card chooses what order to apply them.
2020-08-07 · Wizards of the Coast
The effects of multiple Thought Reflections are cumulative. For example, if you have two Thought Reflections on the battlefield, you'll draw four times the original number of cards. If you have three, you'll draw eight times the number of cards, and so on.

Rulings: Scryfall · Wizards of the Coast