Question

In double battles, if two Pokemon of the same team uses rain dance in the same turn, will it have double effect?

Answer 1

According to Bulbapedia:

Rain Dance will fail if it's already raining. [...] If heavy rain, extremely harsh sunlight, or a mysterious air current is present, the move will fail.

Rain Dance does not work in the presence of some other weather conditions, including rain, which Rain Dance provokes. Therefore it would fail if it were used twice in the same turn.

Hope I helped. :)
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