Card

Mana Reflection

Mana cost {4}{G}{G}

If you tap a permanent for mana, it produces twice as much of that mana instead.

Part of 163 known combos, 5 of them two-card. 4 official rulings.

Bracket

B1 Exhibition — Not in the same deck as its two-card combo partners: Basalt Monolith, Freed from the Real, Pemmin's Aura, Grim Monolith, Palinchron
B2 Core — Not in the same deck as its two-card combo partners: Basalt Monolith, Freed from the Real, Pemmin's Aura, Grim Monolith, Palinchron
B3 Upgraded — Not in the same deck as its early two-card combo partners: Basalt Monolith, Freed from the Real, Pemmin's Aura, Grim Monolith, Palinchron
B4 Optimized — allowed: No restriction beyond the banned list
B5 cEDH — allowed: No restriction beyond the banned list

Two-card combo with Basalt Monolith, Freed from the Real, Pemmin's Aura, Grim Monolith, Palinchron (early with Basalt Monolith, Freed from the Real, Pemmin's Aura, Grim Monolith, Palinchron)

Bracket: Lotus Vault analysis, with Commander Spellbook flags

163 known combos, 5 of them two-card.

Yurlok of Scorch Thrash + Staff of Domination + Mana Reflection
Produces: Infinite black mana for all players, Infinite card draw, Infinite draw triggers
View on Commander Spellbook
Yurlok of Scorch Thrash + Umbral Mantle + Mana Reflection
Produces: Draw the game, Infinite black mana for all players, Infinite green mana for all players
View on Commander Spellbook
Basalt Monolith + Mana Reflection
Produces: Infinite colorless mana
View on Commander Spellbook

2020-08-07 · Wizards of the Coast
If an ability triggers “whenever you tap” something for mana and produces mana, that triggered mana ability won't be affected by Mana Reflection.
2020-08-07 · Wizards of the Coast
The effects of multiple Mana Reflections are cumulative. For example, if you have two Mana Reflections on the battlefield, you'll get four times the original amount and type of mana. If you have three, you'll get eight times the mana, and so on.
2020-08-07 · Wizards of the Coast
Mana Reflection doesn't produce any mana itself. Rather, it causes permanents you tap for mana to produce more mana. If the mana ability of that permanent puts any restrictions or riders on the mana it produces, that will apply to all the mana it produces this way.
2020-08-07 · Wizards of the Coast
You're “tapping a permanent for mana” only if you're activating a mana ability of that permanent that includes the {T} symbol in its cost. A mana ability produces mana as part of its effect.

Rulings: Scryfall · Wizards of the Coast