My understanding is that shadowy disguise buffs direct damage abilities. It shouldn't impact things like mutagen or healing springs. However, it should guarantee a crit on Funnel Health and Sap Essence, which would result in a crit heal for whomever receives it.
The answer is yes, it adds 100% to your spell crit, which will count for a heal if cast. you can see this yourself by casting shadowy disguise then looking at your character sheet
Well.. On PS4 Shadowy Disguise no longer shows +100% to your crit on your Character Sheet but my attacks still deal a crit.
When I tested this with Rapid Regen I wasn't getting Combat Text showing up even though the beams (whatever you want to call them) were coming off. I wasn't with friends either so can't confirm if they were getting crit heals. Maybe it was lagging so I'll try again in a few hours and actually report back this time.
Although, any StamNB with SD and Vigor or Rally should be able to test in the meantime.
Edited by Sunburnt_Penguin on April 1, 2016 8:01AM