Control (Rate of Decay) follows the usual rules for mass limits. It can increase the rate of decay by 10% x (level squared) or decrease it by 10% per level.

Common Modifiers [+150%] 
    Persistent [+40%] 
    Extended Duration (Permanent) [+300%] 
    Based on Activation Roll [+5%] 
    Full Decrease Only [-80%] 
    Reduced Duration (1/60) [-35%] 
        Applies to the ability to alter decay, not the Persistent effect 
    Only Works on Dead Bodies [-40%] 
        Includes mummies and zombies 
    Magical [-10%] 
    Spell Components [-30%] 
        Must say "stop decay" in Latin 
        Must gesture with hands 
        Must hold a drop of vinegar 
Level 1 [205] 
    Control (Rate of Organic Decomposition, Rare) 1 [25] 
    Control (Rate of Organic Decomposition, Rare) 9 [180] 
        Doesn't Increase Mass Affected [-50%] 
Levels 2+ [+20/level] 
    Add Control (Rate of Organic Decomposition, Rare) 1 [20] 
        Doesn't Increase Rate Control [-50%] 
        Further Levels increase this by 1 level