Does a replacement effect that doubles mana apply before or after other mana doublers like Mana Reflection?

When two or more replacement effects would apply to the same event, the affected player (or the controller of the affected permanent) chooses the order in which they apply, per CR 616.1. This is crucial because the order you apply mana-doubling replacement effects can dramatically change the final output.

Both Mana Reflection (which doubles mana produced by permanents) and effects like Extraplanar Lens or Vorinclex, Voice of Hunger operate as replacement effects that modify a mana-producing event. Since they are all replacement effects modifying the same event — the production of mana — the player who controls the source of mana (or the affected player) chooses the order of application per CR 616.1 and CR 616.3.

Mathematically, the order does NOT change the final result when both effects simply double the mana, because 2× then 2× equals 4×, same as 2× then 2×. However, if the effects are not pure doublers (e.g., one adds a fixed extra mana instead of doubling), then order matters significantly and the player should choose the most advantageous sequence.

Example: You tap a Forest that normally produces {G}. Both Mana Reflection and Extraplanar Lens apply. You choose to apply Mana Reflection first (producing {G}{G}), then Extraplanar Lens doubles that to {G}{G}{G}{G}. Alternatively, applying Extraplanar Lens first then Mana Reflection yields the same {G}{G}{G}{G}. Here order doesn't matter — but if one effect instead added a flat {G} rather than doubling, the order chosen by the player would change the total.

The key rule is CR 616.1: if two or more replacement or prevention effects try to modify the same event, the affected player orders them. There is no inherent priority between mana doublers — player choice governs the sequence.