If you want it to be true to Faxanadu, you should put a bottle of poison that takes away hearts into the drop set. It would look exactly the same as the elixir, of course.
I tried to cheat my way out of using global variables today and everything went wrong. Now this boss dies in one hit for mysterious reasons.
I could do that, although I remember it being glitchy last time I tried having negative life recovery items. I haven't tested with 2.5.5's Launcher (2.5 Final/Build 24) but I know the ZQuest that came with the 2.5.4 Launcher had some major bugs with those items. I don't know if they're fixed in the stable 2.5, but the glitches were:
1. Suppose I have an item take away 1 heart. Without having "gradual" checked, if I had say 1/2 heart left, it would actually reset my life to full. If I had the exact amount of life however, I got a game over as normal.
2. With the items set to gradual, I noticed that the loss would actually continue to affect me after a game over. For instance, say the poison jar takes 5 hearts away gradually and my life is at 2 hearts. I'll die, game over, but when I continue, I lose another three hearts.
Again, I haven't tried this in 2.5 build 24, but I remember having things like that act funny. What would be even more faithful to Faxanadu though would be if it would say "I've touched poison." every time you pick one up and it knocks Link back as if he got hit. Meh, I don't know to be honest. I remember one junk quest I had with 2.5.4's Launcher (again, don't know if that was a Beta or RC build of ZQuest) I had enemies drop poison jars that gradually hurt Link for a full heart. I also had a schmuck bait shop at the start that eggs you on into buying a potion that actually deals 3 hearts of damage to you over time, killing you if you're stupid enough to buy it. I remember making a lot of god-awful quests in that bug ridden mess of a ZQuest build. That and I didn't know how to make custom enemies or items at the time, so I just overwrote existing enemies. How about 5-way magic shooting Stalfos that can only be killed with bombs and are stunned by reflected magic that moved at 150 Step Speed but had a very slow walk cycle?