I thought up this creature while I was pondering on a big bad for the story dungeon I'd formed for my brother's character, a Dragonborn Warlock faithful to Bahamut, but Patron'd by a nightmare-drinking, fearthirsting Night Serpent. The dungeon theme was a temple to Tiamat, built in the basement levels beneath a destroyed temple of Bahamut... and upon realizing that there were five 'classic' colors to the chromatic dragons, and five heads base on a hydra, I started thinking evil thoughts. And came up with the Chroma Hydra... a terrible beast of ritual experimenting, created when the adherents of Tiamat captured a live Hydra and, after removing one of its heads, injecting the stump with dragon blood of varying broods. The end result: a terrifying monstrosity with five chromatic dragon-heads, a little weaker physically for all the experimenting done to it, but empowered with the fearsome might and deadly breath of the dragon blood infused into its being.

https://www.dndbeyond.com/monsters/153098-chroma-hydra

One legendary actions should be a bite attack. When Forced Inhale is coupled with the secondary recharge, both feel bizarre, you're creating a problem and then fixing it, perhaps make the recharge 6. And remember to attach costs to the legendary actions.

The breath weapons seem very powerful, as does the chromatic breath (chromatic breath still has language from disintegrate). Have you balanced this monster's CR based on Creating a Monster in the DMG?

Hmm... a bite attack would be okay. The reason I had the recharge at 5-6 was because it requires two successes before it can utilize its multibreath again. As for the breath weapons themselves, I'd taken the areas from the young dragon breaths, and the damage roll from the weakest damage-wise of the five. Could tone it down. The chromatic breath, being rare and detrimental to the hydra, is meant to be strong... I naturally leant to Disintegrate as a base, owing it as the flagship 'this is dangerous' spell that isn't of one element, but could change it to something else.

Giving the chroma hydra a bite attack makes a certain amount of sense, there's all these heads, what are they doing? Normally, legendary actions have a perception check, an attack, and a special ability. However, they often cost 1 or 2 legendary actions, make sure the cost is included.

The description for Chromatic Breath has the sentence "This spell automatically disintegrates a Large or smaller nonmagical object or a creation of magical force."

I understand the want for two successes but there's a much simpler solution. The probability of a 5-6 recharge is 0.33, the probability of your recharge is 0.11, if you use Forced Inhale 3 times, as I assume it costs 1 action, the probability increases to 0.8. If you wanted a lower recharge probability, try Recharge 6, that will have a probability of 0.17.

Edit: I notice you use different DCs for different breath weapons, the perception skill has a different proficiency bonus than the attacks, the constitution bonus to the hit points does not match the constitution modifier and Chromatic Breath does not have an average damage.

Also, I think the current CR is a little high, it should be around 9 or 10.

Hmm... I like the Recharge 6 switch... and I'll make the Focused Breath ability use up its Legendary Actions, as all the living heads take a moment to try and recuperate. Also fixed the wording on the Chromatic Breath to get rid of the spell mentions. I also fixed the DCs for the other basic breaths to match the average '14', with the exception of the Chromatic Breath, which being a directed breath weapon rather than an area breath, would be faster and more difficult to dodge.

I'm open to suggestions for numerical fixes for the hit points and the perception skill, though. I'll publish a fixed version when I have this info. Not afraid to make mistakes so long as I can learn from them. :3

DCs are typically 8+proficiency bonus+relevant ability modifier. The proficiency score appears to +4 as does the Constitution modifier, bringing the DC to 16. All breath weapons would have the same DC, no question. You could increase the Constitution to 20 but that would increase the DC as well. Perhaps give it a few more hit dice and calculate the constitution bonus as number of hit dice x constitution modifier. Perception should go up to +4. If you change it to recharge 6, I don't think Forced Inhale is necessary.

When you change the monster next could you republish it so I can continue to follow along with the most current version?

Okay, think I've gotten it. I decided the hit points could be lower than a natural hydra, so adjusted for the lower constitution modifier while keeping the hit dice. Brought up the breath DCs to match, as well as the Perception, and nixxed the Forced Inhale.