Orochi

Eight heads and eight tails and a body that covers eight valleys and eight hills, with moss and cedar growing along its back and its belly worn raw and red. It has taken a daughter from the same family every year for seven years and there is one left. Everyone who has gone up the valley with a sword has stayed there. The thing that worked was not a sword. It was eight vats of very strong sake, one at each of eight gates, and the patience to wait.

Eight Heads: piercing, melee 20 ft, +7 to hit, 3d8+6, three times each round from three separate heads, and it can strike three different targets at three different points of the field. Sweep: 30 ft, save Dex Quick, fail save roll 3d8+6 bludgeoning as the tails come round, cooldown 2 rounds.

Eight of Everything: it cannot be flanked, surrounded, blinded or restrained, and effects that target one head accomplish one eighth of what the caster wanted. Sake: set out strong drink where it can reach - one vessel per head is the traditional arrangement - and it will drink, all eight heads at once, and it cannot stop itself. After one round of drinking it is at Disadvantage on everything; after two it is asleep. Asleep it can be killed by anyone. Reduced to 0 HP while awake, which nobody has managed, it dies normally.