Question

I'm not sure if it's just a sableye exclusive ability. Stall seams like the worst ability ever next to defeatist or slow start.

Answer 1

Stall is just a sableye exclusive ability. But yeah... its pretty terrible. The only advantage I can think of is that payback will almost always be full powered because it will always be going last but like smogon says (in my source) its not worth always going last. It also can be used with skill swap but must be done in doubles/triples because sableye cannot learn skill swap. So it really has no use and especially since sableye has prankster which is amazing especially since sableye has the moves (will-o-wisp, taunt, recover, etc.) to abuse it with. So it is pretty much useless. Stall's usage on smogon is less than 2.12% compared to pranksters's 97.88% usage in UU. So yeah nobody should ever use stall on sableye when it has prankster.
Source: http://www.smogon.com/bw/abilities/stall

Answer 2

Yes there is. It could be useful for moves like Payback that get stronger when used last. Also may be useful for skill swapping etc.

Source: http://pokemondb.net/pokebase/35671/is-stall-a-useful-good-ability

Answer 3

You can make it hold zoom lens, which makes your accuracy 20% higher when you move later. That can raise its accuracy of Will-o-Wisp from 75% to 90%

Comments

it would be 95%

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you shouldnt add 20%, you should do x1.2