Water Hornet:
Shadow:
1) Can water from the Water Summoning Chalice and heat from the no-floor room be used to boil a tea for Gnallia?
2) Can Curing and Psy-screen be used together to lower the chances of Agdana addiction (for example 25% -> 10%)?
1) Sure, if you're willing to wait for the twenty or so minutes it'd took for the tea to be ready. Although I'd suggest using fire of your own making rather than the heat from the lava - that's hot enough it has a chance (which would be rolled) of permanently damaging the chalice: golds melts pretty easily, you know. :)
2) Can't think of a way right now, but if you can figure out a combination of Disciplines and Improvements that might manage so, put it up and I'll give you a ruling - although expect that to be a really unlikely thing to be doable; if it was in any way easy to make Adgana lose its additiveness, it'd have been done before now, since a lot of people would be looking for it. Managing such a thing would be a worldwide-renown-worthy feat, and while I'm always open to your improvisations, I don't think that'd be doable without having the lorecircles of Solaris and Moon at a very minimum (and Light would probably help).
I hope those aren't too diseheartening as far as answers go?