For the first time ever in a decade I have finally defeated the Necromancer as well as beating Insane Mode all on my own, this fight has a very huge difficulty spike on Insane Mode and especially if you're doing it alone.
Vanilla+ comes with a few QoL changes like Auto Potion being a thing in single player when your HP reaches 0, and sometimes would refill automatically upon entering a stage, the final level also has 3 map points which takes you to the first three bosses which honestly act like checkpoints, so if you lose to Necromancer, you can select his area and start there rather than starting from the beginning of the level where you have to deal with the Cultists.
You can download the mod here: gamebanana.com/mods/441934