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If you tap a permanent for mana, it produces twice as much of that mana instead.
If an ability triggers “whenever you tap” something for mana and produces mana, that triggered mana ability won't be affected by Mana Reflection.
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.
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.
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.
