I See Curently no way to Beat the Final Boss from The Master Tree I Heard Already from a Level 4 Sword and a Red Tunic but the problem is That on All Ways This Red Flame Blocks The Way I cant go Deeper in the forbidden Dungeon or make more Progress in The Trading Quest as i Must Deeper in The Death Mountain Sumit for it
You can get rid of the flames by going back to check a cave in West Hyrule. But yeah, the final boss can be brutal with just the blue ring.
And unfortunately you do have to complete the trading sequence in order to get the Red Ring, which is somewhat of a big flaw in retrospect.
I'll make ring upgrades less missable in my later quests.