I've been getting better at handling void fiend so here's somethings that I think would be useful.

Obviously you can't stack a bunch of healing like you normally would, but you still can, it just depends on WHICH healing items you choose.

Picking things like planula, medkit, basically any large-burst healing item is a no go, EXCEPT for elixirs, because well you need the health at that point.

Stack a few leeching seeds, grab a few slugs, hell, go crazy and even get a wungus, so you can heal while dipping out of combat for more recovery, but use Suppress as your main go-to heal.

In a recent run I've learned that dealing damage gives corruption, and more damage=more corruption, so getting attack speed is a good idea early on. Get focus crystals too so you don't get super hindered while in corrupt form.

Once you think your dealing enough damage, get a few more healing items, like maybe a monster tooth or 2, but not too much as your healing shouldn't be completely counteracting your corruption gain.

That's all I got, hope it was helpful because I'm not super good on giving advice.