Biroo is usually found at the brightest moments of the day and has an incredible fear of the dark. It runs away from its own shadow constantly and nobody but Biroo knows why. Some speculate that Biroo's shadow is alive, but some simply think it's because Biroo is known for its cowardice.

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This is due to Biroo usually keeping to themselves and being startled very easily. They're often compared to Wimpod because of this. However, some Biroo change drastically in behavior when befriended by a trainer, becoming significantly more confident than they ever could be alone, to the point where some even stop being scared of their shadow. They usually stop being afraid right before evolution.

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Infiltrator allows Biroo to get around any wall, meaning Light Screen, Reflect and Safeguard will not keep you safe from Biroo. Some Biroo don't get confident before evolution and will have the ability Wimp Out, which makes them flee from battle after dropping below half HP. Its Hidden Ability is said to use the shadow as a partner to keep the opponent in place so they cannot run away.