[Powers] Building Temporary Add-on Effects

[Desthro]

If I am not mistaken, using enhancements and limitations to apply to other enhancements/limitations is a matter of multiplying the modifier with the enhancement or limitation you are using. Examples would include limiting enhancements based on certain accessibility. Like say, your ability has an AoE effect, (+50%) but the AoE effect only works when you are standing in a vat of Everyone's Buddy Brand Peanut Butter (Accessibility -80%), it is a net +10% modifier (-80% of 50% is 10%) IF your ability works without the AoE effect generally. This requires a little finesse, as not everything works as intended this way, and you need to use some common sense on what is okie dokie and what is not.

An attack that reduces DR but heals more quickly would require some tinkering, but I think you are on the right track. You COULD try and extrapolate a "reduced duration" modifier in terms of the recovery period for healing the DR, and it seems you have done that with a value of ~ -70%. This would make the no-wounding effect even more limiting, 70% of 50% is 35%, 50%+35% = 85%, and I'd snowball an attack that lowers DR for minutes over days at about that range. -85% caps at -80%, and 2 points per 1d of exceedingly limited corrosion damage seems pretty comparable to an Affliction that removes DR.

Of course, I'd just use an affliction that removes DR ;)
Actually... I'd consider an affliction that inflicts negative DR to be reasonable... there's no reason that DR can't scale inversely. Striking ST is comparable. =)