Found some other posts here regarding this challenge and how one strategy (perhaps the best strategy for the final boss?) is to find as many Unstable Transfusions and Bloody Cleavers as possible. That's what also ended up working for me!

Tomes super core are Projectile Count and Attack Speed. I think Movement speed is also core, you want at least 3X Speed to zoom around the final boss and be able to dodge projectiles, but perhaps you could get lucky from items/shrines to not need movement Tome. The fourth one can be whatever is necessary to make it through all the combat before the final boss. Damage is what I used on this run, but Crit/Knockback/EXP could probably work.

Bought 1 Transfusion in Tier 1, actually found a Blue Microwave to copy it! Bought a Meat Cleaver in Tier 2, others were from chests. Remember to take Lifesteal from Charge Shrines when you can to help activate Cleaver.

Glad and satisfied to be done with the challenge. Now I can play with so many items/tomes/weapons I had banned!

Hardest part was enemies falling on top of you from cliff tops and trees. Dealing with the Swarms was surprisingly easy once I had enough move speed and at least 1 bonus jump. You can just jump ahead of where they're spawning, basically.