How much weaker does a move get when it hits all the opponents in a double or triple battle?

Question

For exemple, Water Spout's power is 150 against one opponent. How much would it be against two or even three?

Answer 1

In Gen 3, it was 50%, but every other game after it is 25%. So, Water Spout would have a base power of 112.5 then.
Source: https://m.bulbapedia.bulbagarden.net/wiki/double_battle

Comments

Then when? Both in double and triple battles?

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It is true for any move that damages more than one target, but not every single pokémon like Earthquake.

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Yeah, I checked your source. Thanks!

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No problem