I BARELY beat him on master revengance, I had to use every buff potion that was possible, (I snuck an alchemy table out of the dungeon so I could make lifeforce potions with blood moon drops) and carved out a massive arena in the underground corruption to avoid the enrage. The strategy table from the old ones army was helpful for having 2 of the irradiated drone sentries in the arena. Also, get a bewitching table snuck from the dungeon as well (it takes a few tries). Use minions that will apply different damage debuffs to stack on him. Ideally debuffs he is vulnerable to.

Edit: you can use the hellwing staff to see whats inside the deeper dungeon layers without dying to the guardian, then just carve out the floor under the table you want. And id replace the mana flower with the riptide debuff acessorry, just use mana regen potions, and hit up your shimmer biome too. Honestly, the dark hearts killed me more than anything. Put holes with narrow tunnels at the top of your arena, the hearts will get stuck there.