Was having a really good Greed run as Azazel when I ran into Punker... which really shouldn't have been a problem, except that I had two items that gave "your first tear in a room does massive damage".

Apparently those items stack, and apparently Punker uses the boosted damage to determine his health scaling. The result was a Punker with a health bar that would make Ultra Greed blush; fifteen or so full brimstone hits took off less than 10%.

Not sure if there is any way to fix this interaction, but I thought I'd report it anyway - if for no other reason than so that other people are aware of the risk of items like that.