A: We’d consider any cards which change the meaning of numerals on a card to be mutually exclusive to each other. Only one of them can be in play at a time, so if one is out, and someone plays a different one, the previous one would be discarded.

Inflation (Fluxx 5.0)(also available as a promo card)
Double Vision (Fluxx Remixx, Drinking Fluxx, More Rules promo pack)
One, Two, Five! (Monty Python Fluxx)
Increment All (Math Fluxx)
Mathematical! (Adventure Time Fluxx)

Note that you’ll find almost all of these (except for 1,2,5) on the same line in the Fluxx card comparison spreadsheet, since we consider these to be kind of variations on Inflation.