Official Move Approval IV

[Mark]

Combat Acceleration- Requires Physical Strength, Burst Movement (300 OM)

Kelly's 'neural throttle' allows him to increase his cerebral processing speed for brief periods. Correspondingly, the speed at which he attacks and defends also increases, though the force with which he strikes remains unchanged. While using combat acceleration, he can perform basic (non-Move) attacks, evasions and defenses as though his SPD were doubled. As with normal burst-movement, this effect only lasts for a single second, with a minimum of one second between uses. Also as with regular burst-movement, use of combat acceleration is much more draining than attacking, evading or defending normally, and frequent use will wear him out quickly.

Approved.

Alright, I'm going to make some edits. 

Decay - 300 - Debuff, Ranged Proficiency, Area Effect Proficiency: 

Igniting his horn, King Sombra will form a gas cloud. This takes about 10 seconds for him to do so. But there's something unique about this cloud because it doesn't damage an opponent. What it instead does is that it attacks their weaponry similar to how acid would eat away metal, this cloud rusts their weapon they have on hand. This reduces the damage that their weapon does by one damage level. 
This requires him to stand perfectly still, and while using or charging this move he cannot defend, or attack. In short, when he is preparing or utilizing this move he is entirely helpless and incapable of moving his body, or using his moves at all. Furthermore this is very draining on his stamina, which is why he can only do it once every 2 minutes. This has a duration of 15 seconds, and a range of 55 feet from him in any direction. The cloud is not something he likes to use often because of how draining it is on him to use.

I'm unsure what you mean by 'one damage level'. I would phrase it instead as "deal somewhat less damage" or something similar. Also you still need to address whether leaving the cloud cancels the effect.