Fusaiyama no Akuma (5e Creature)
From D&D Wiki
Fusaiyama Akuma (Kazan Akuma)
Gargantuan fiend, chaotic evil, any evil or chaotic neutral.
Saving Throws Strength +16, Con +14, Cha +7
Magic Weapons. The oni's weapon attacks are magical.
Regeneration. The oni regains 20 hit points at the start of its turn if it has at least 1 hit point. Thunder damage stops this regeneration.
Multiattack. The Fusaiyama Akuma makes two attacks, either with its Zhanbatao or its Kanabo.
Massive Zhanbatao. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 30 (4d10 + 10) slashing damage.
Massive Kanabo. Melee Weapon Attack: +14 to hit, reach 20 ft., one target. Hit: 30 (4d10 + 10) Bludgeoning damage.
Mountain Demon Breath (recharge 5-6). ranged damage in cone up to 40 feet. all enemies must roll dexterity or constitution save Dc. 20 or take 30 (6d6+10) elemental damage from the Ghost-fire fury chart
Mountain Demon Fury (Recharge 5-6). The Akuma no Kazan flys into a wild rage and either a Whirling Flames or Freezing Winds erupts from his frame. Each creature in that that attacks the Oni DC 19 Dexterity saving throw, taking 6 (1d6+2) elemental damage on a failed save, or half as much damage on a successful one. This Fury lasts for 1d6+2 turns and the Oni can now add 1d6+2 Fire or Cold damage to every attack it makes. This effect can not be dispelled. Each turn this Fury can switch to the opposite element especially after taking the damage the Akuma is Vulnerable to this also Gives the Kazan Akuma damage 1d4+1 Fire/Cold on his weapon attacks. When the Mountain Demon Fury Cloak is Fire the Kazan Oni becomes weak to Cold and When the Mountain Demon Fury Cloak becomes Ice they become weak to Fire. The Fury lasts for 1d4+2 turns and it stacks. So if the Mountain Demon Fury Recharges and they spend it the Cloak damage goes up to 2d6+4-->3d6+6-->4d6+8-->5d6+10 and the weapon damage goes up 2d4+2-->3d4+4-->4d4+4-->5d5+5.
These titanic Akuma look just like a Gargantuan Two Headed mountain oni with one head being that of a Blue Yuruyama no Oni and the Other head being a Red Akaiyama no Oni, so these creatures are famous for quarreling amongst each other with the Red Oni head being more Impulsive but Expressive and the Blue Oni head being more logical but repressed his skin. Each head can have an unusual number of horns and eyes, one eye or three, one horn or three for example. One side of their body is dark crimson red and the other a dark midnight blue but running down the middle and all over the body are various purple stripes like a tiger. During Combat these creatures agree to settle their arguments and focus on destroying their enemy on hand. The Fusaiyama Akuma (Kazan Akuma) have a massive purple fanged maw in their belly and they sometime's enjoy hurling foes they have grabbed into their stomach maw. These are the kings of the mountain oni's and it illustrates how an Oni can become a powerful Rakshasa or Asura lord with enough time, murders and other heinous dead committed to their might. Tribes of Oni and Bakemono will generally find one and worship it, giving them food as slaughtered game or even sacrificing Saru Bakemono or Yokai to feed these mighty beasts. Armies of Bakemono and yamaoni might get slaughtered trying to breach a great wall or castle but they will roar in defiance when the Akuma no oni appears and simply reduces the defenders walls to rubble. Thankfully these massive titans are rare and it takes hundreds of years for regular feral mountain oni to ever get so large.
Sometimes the titanic Fusaiyama Akuma or Kazan Akuma get tired of it's mountain oni brethern and their barbaric ways and they simply go out the the high mountains or secluded vales to sleep, eat mountain goats and raise flocks of cattle and make wine from wild grapes. Strangely enough these shepherd Akumas can be recruited by Samurai and human warriors to defend their settlements from rampaging hordes of Oni, Bakemono and others. If the Samurai's and heroes can just get the heads to stop bickering for a moment.