What is a mon's evasion under this condition?

Question

Just out of curiosity, if a Pokemon has sand veil, sand is up, has brightpowder and used double team or whatever move that boosts evasion up until it can't boost anymore, what is the evasion percentage at that point? Is it a hundred percent or ninety something? I also wanna know about the situation where sand is up and when it is gone, what is the evasion percentage in each situation? Also, if there are any significant differences in mechanics by each generation, please mention it - not counting the part where weather is no longer permanent. Lastly, is there a situation where a Pokemon cannot be hit by any attack via evasion, not counting stuff like aura sphere?

Answer 1

A Pokemon at +6 evasion (max boosts) and no other modifiers has a 1/3 (33%) chance of being hit by a normally 100% accurate move in every generation except gen 1. In Gen 1, +6 evasion reduces the accuracy of moves down to 25%, but items and abilities do not exist to lower this chance any lower.

Sand Veil, when activated, multiples the accuracy of moves by a factor of 4/5, turning 100% accurate move into 80%.

Brightpowder reduces the accuracy of moves by a factor of 9/10, so 100% accurate moves become 90%.

A Pokemon at +6 evasion and holding brightpowder will reduce 100% accurate moves to 30%.
A Pokemon with active Sand Veil, +6 evasion, and a brightpowder will reduce 100% accurate moves to 24%.

It is not possible to reduce a move to 0% accuracy. The absolute worst-case scenario would be trying to hit a move with 50% accuracy under these conditions (this is the lowest base accuracy of any move in the game outside of OHKO moves, which bypass accuracy modifiers). In this case, you could get as low as hitting only 12% of the time.

Source: Bulbapedia

Comments

So the evasion boosts don't stack with one another? Or does it stack but diminishingly?

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Evasion boosts do stack, but they're multipliers. You can't get 0 by multiplying non-zero numbers.