First of all, I'm going to put this out here. Stop it with new abilities!!! New things should only be created if needed. We have plenty of abilities that would work with CAP10.
But mostly, I want to talk about Download. I certainly do not think Download would be broken on CAP10. Its actually somewhat useless against some threats. Lets go down the list of OU's, seeing what gets boosted. A question mark will be put by those who have a difference of 5 or less between Base stats.
Scizor: 100/80 Defenses=SpA
Tyranitar: 110/100=SpA
Salamence: 80/80=?
Heatran: 106/106=?
Latias: 90/130=Atk
Rotom-A: 107/107=?
Gyarados: 79/100=Atk
Jirachi: 100/100=?
Metagross: 130/90=SpA
Gengar: 60/75=Atk
Swampert: 90/90=?
Lucario: 70/70=?
Infernape: 71/71=?
Starmie: 85/85=?
Blissey: 10/135=Atk
Gliscor: 125/75=SpA
Azelf: 70/70=?
Magnezone: 115/90=SpA
Skarmory: 140/70=SpA
Vaporeon: 60/95=Atk
So lets go down this list. Scizor is not something I see CAP10 having a specific set for, but if you do switch in you likely will gain an advantage. But against T-Tar, your actually gaining the WRONG attacking stat-no way you take that thing on with Special moves. Mence often runs abilities that lower its SpD, but with a pokemon that often uses Download, it would be smart of Mence to change it up-there is no major disadvantage to having a lower Def, just -SpD is prefered (and also on the analysis). Heatran is in the same boat as Mence. Latias is a good pokemon to have Download against. Physical electric and Ice are pretty weak-but avalanche is strong enough to give CAP10 an OHKO against Latias. So for anything that is gaining Atk-its mostly useless on CAP10. Rotom-A normally runs Def EVs... but switching CAP10 in on Rotom is kinda dumb-you don't have much of an advantage against it, and you risk being burned or something. Gyarados, again you get only Atk, but this time, its useless-any set countering Gyarados will want to use a different ability as T-Bolt kills him real good. Jirachi is essentially a coin flip-not reliable enough to make CAP10 an all out sweeper. Metagross is another pokemon Download is significantly helpful against-it makes thoe Earth Powers that much stronger. Gengar you are getting atk... which is worthless.
So at the half way point lets recap: Salamence, Heatran, and Jirachi are to risky to use Download against and against T-Tar, your boosting the wrong stat. Gyarados and Gengar give you your worse stat boost, and it isn't needed. Rotom you won't be switching in on. So that leaves Latias and Metagross as pokemon that help CAP10 do its job, and one (Scizor) that can be used as set up fodder. This isn't broken at all. Download is a fine ability for countering certain threats, but it is not reliable enough to make a sweeper with. But lets take a look at the next ten.
Swampert will always have max Def, but he also will always have STAB EQs... not fun for CAP10. Lucario will always have identical defenses exept on uncommon mixed sets, so he just makes for another unreliable pokemon to set up on. Infernape is along with Mence and Heatran in the switch the lowered defense to screw with CAP10 boat-definately not reliable. Starmie normally doesn't run defense outside of HP, so its certainly not fodder. Blissey is lol. Gliscor, Skarm and Magnezone can all be used as set up, so there's something I will conceed on, but Vaporeon is useless, and Azelf is just like Mence et al.
So in conclusion, Download is vital to counter Latias and Metagross, useful for Mixed sets against other mixed threats, and might make Physical CAP10 more of a threat. I don't see anything wrong with that. In fact CAP10 could use a little offense. 80 base stats are weaker than you think... Do you see Tentacruel (who is actually quite fast) sweeping anything? Or even being any sort of offensive threat? CAP10 needs that little boost that Download provides.
But mostly, I want to talk about Download. I certainly do not think Download would be broken on CAP10. Its actually somewhat useless against some threats. Lets go down the list of OU's, seeing what gets boosted. A question mark will be put by those who have a difference of 5 or less between Base stats.
Scizor: 100/80 Defenses=SpA
Tyranitar: 110/100=SpA
Salamence: 80/80=?
Heatran: 106/106=?
Latias: 90/130=Atk
Rotom-A: 107/107=?
Gyarados: 79/100=Atk
Jirachi: 100/100=?
Metagross: 130/90=SpA
Gengar: 60/75=Atk
Swampert: 90/90=?
Lucario: 70/70=?
Infernape: 71/71=?
Starmie: 85/85=?
Blissey: 10/135=Atk
Gliscor: 125/75=SpA
Azelf: 70/70=?
Magnezone: 115/90=SpA
Skarmory: 140/70=SpA
Vaporeon: 60/95=Atk
So lets go down this list. Scizor is not something I see CAP10 having a specific set for, but if you do switch in you likely will gain an advantage. But against T-Tar, your actually gaining the WRONG attacking stat-no way you take that thing on with Special moves. Mence often runs abilities that lower its SpD, but with a pokemon that often uses Download, it would be smart of Mence to change it up-there is no major disadvantage to having a lower Def, just -SpD is prefered (and also on the analysis). Heatran is in the same boat as Mence. Latias is a good pokemon to have Download against. Physical electric and Ice are pretty weak-but avalanche is strong enough to give CAP10 an OHKO against Latias. So for anything that is gaining Atk-its mostly useless on CAP10. Rotom-A normally runs Def EVs... but switching CAP10 in on Rotom is kinda dumb-you don't have much of an advantage against it, and you risk being burned or something. Gyarados, again you get only Atk, but this time, its useless-any set countering Gyarados will want to use a different ability as T-Bolt kills him real good. Jirachi is essentially a coin flip-not reliable enough to make CAP10 an all out sweeper. Metagross is another pokemon Download is significantly helpful against-it makes thoe Earth Powers that much stronger. Gengar you are getting atk... which is worthless.
So at the half way point lets recap: Salamence, Heatran, and Jirachi are to risky to use Download against and against T-Tar, your boosting the wrong stat. Gyarados and Gengar give you your worse stat boost, and it isn't needed. Rotom you won't be switching in on. So that leaves Latias and Metagross as pokemon that help CAP10 do its job, and one (Scizor) that can be used as set up fodder. This isn't broken at all. Download is a fine ability for countering certain threats, but it is not reliable enough to make a sweeper with. But lets take a look at the next ten.
Swampert will always have max Def, but he also will always have STAB EQs... not fun for CAP10. Lucario will always have identical defenses exept on uncommon mixed sets, so he just makes for another unreliable pokemon to set up on. Infernape is along with Mence and Heatran in the switch the lowered defense to screw with CAP10 boat-definately not reliable. Starmie normally doesn't run defense outside of HP, so its certainly not fodder. Blissey is lol. Gliscor, Skarm and Magnezone can all be used as set up, so there's something I will conceed on, but Vaporeon is useless, and Azelf is just like Mence et al.
So in conclusion, Download is vital to counter Latias and Metagross, useful for Mixed sets against other mixed threats, and might make Physical CAP10 more of a threat. I don't see anything wrong with that. In fact CAP10 could use a little offense. 80 base stats are weaker than you think... Do you see Tentacruel (who is actually quite fast) sweeping anything? Or even being any sort of offensive threat? CAP10 needs that little boost that Download provides.