The Mantigon

A failed ritual by a cult of Tiamat caused the essence of the five colored dragons to fly out into the continent of Geran, settling in environment and bodies that suited them individually. The essence of the green dragon found its way into a particular big and ferocious manticore in the Great Forest. In the months following the possession of the green essence, the manticore started changing, growing, becoming venomous, and covered in green tumor-like boils. At the base of the manticore’s neck grew a particular big and nasty looking boil, almost yellow at its core. Slowly the green dragon is overtaking its host, both body and mind, ultimately the original host dies.

Transformative Fortitude

Mechanically when the first form of the Mantigon hits 0 HP, any excess damage doesn’t carry over, and all ongoing effects stop. Roll either new initiative for the new form, or new initiative for all.

The transformation

After the Mantigon's first form hit 0 HP it plummets to the ground if flying, all the green tumor growths bursts in a cloud of toxicity 30ft out from the Mantigon, creatures in this range have to make a DC 15 constitution save or become poisoned. The affected creatures may retry the save at the end of their turn, the poison end after 1 minute. Out from the large green neck tumor unfolds a long necked green dragonhead, green and yellowish scales spread across the body in seconds, the coarse fur rotting away. The wing bones crackingly stretch as they extend, the skin rips and tears leaving large holes. The tail-end grows heavier, the spikes are now half covered in dark-green scales. The Mantigon grows even larger. Any swallowed creature slips out of the unconscious manticore head. Roll initiative.

Tactics

The Mantigon will prefer to ambush the people coming to its hunting grounds.

1st stage: More animalistic, and unwilling to fly away, but fight till "death". Flies around at distance, into 60ft. range, and back to cover, trying to use trees as cover, concentrating all tail spikes on one unarmoured or ranged target. Also roars for minions in draconic: ”Spawn, come feast!” it will use legendary reactions to attack anyone nearing it. If seeming to lose the ranged battle, at around half HP, the Mantigon will swoop down to swallow a damage dealer and fly away to let the swallowed be consumed.

2nd form: Begings with roar when most hostiles are within range, it will fight smarter and be willing to retreat, focus on healers if any or damage dealers. It will stampede towards ranged damage dealers or healers, if they’re out of reach it will loogie instead. Any fliers, or creatures crawling around in trees it will loogie.

Legendary Reactions

Legendary reactions are different from regular reactions that instead of 1 per round, the Mantigon have 1 legendary reaction per turn. The idea is that unlike legendary actions, the PCs can learn what the reaction triggers are and adapt accordingly. In this case the Mantigon shoots at anyone nearing it and attacking it at range, however due to limited ammunition, relative short range of 60ft., PCs can either try to stay at long range, or if given the opportunity keep it grounded.

References and non-fluff concept explanation

Some of the mechanices are taking from these posts:https://www.reddit.com/r/DnDBehindTheScreen/comments/6gveal/big_boss_solo_inserts_or_plug_and_play_features/

http://theangrygm.com/return-of-the-son-of-the-dd-boss-fight-now-in-5e/

Tail spike ammunition

The first form of The Mantigon have 24 tail spikes, they regrow every day, after a long rest.

Essence of the dragon

In the original campaign The Mantigon is from, the essence of the dragon color moved into whatever creature killed it, as it generally tried to find strong creatures as hosts. The new hosts will at first become sick as if poisoned, only curable by a greater restoration, which temporarily stops the essence from taking over. If the host of the essence is somehow killed without finding a new host immediately, it will fly around freely to try to find a host at a different place later.

Environment / battlemap

The Mantigon fight in the original campaign was in a forested area with lots of difficult terrain in form of bushes and undergrowth and several large redwood trees together with smaller trees dotted around, with a nearby swamp lake. The idea for tactics being, the Mantigon could fly out from total cover of the trees attack, and back into cover. Normally it will try to escape if damage too much, but due to being possessed with the essence of the green dragon, it will fight till the death of the first from. While in its second form it will be quite willing to flee into nearby water source and swim down and away from threats.

Origin of the Chimera

Seeing as the combined green dragon and manticore slightly resembled a chimera, and the corrupting nature of the dragon essence, in the original campaign and setting, the Mantigon had spawned the first chimera into the world, of course all the chimera have green dragon heads, rather than red. The hatchlings can join the fight as minions.