A monster for a campaign I'm planning

[Crow_Nightfeath]

So I'm building a monster known as Gaftonoshu,I got the name and idea from a very old anime. In the anime Gaftonoshu is an 8 headed dragon that one of the family's use as their house crest. The middle two heads forming a yin yang. And that is literally all the information on what Gaftonoshu is.

So that gives me some liberties with how to do it. I decided to kinda copy Tiamat a little, but with a total balance of alignment becoming Neutral. So the heads are Radiant dragon, Shadow dragon, Forest dragon, Sky dragon, Sea dragon, Underworld dragon, Time dragon, and Vortex dragon.

I was just planning on its size being something like all of them put together hence the colossal +, but then comes the part I'm having troubles with, what would the physical stats of this thing be? Mental stats I was just going to leave as each head's. I'm looking for some good ideas on how to come up with the physical stats.

Don't worry about how this thing is supposed to be defeated I've got that figured out.

[Zaq]

Sounds like you’re kind of making things up as you go anyway (which is 100% fine as long as we’re honest about it), so I don’t think that there’s really necessarily a “logical” way to implement this.

What power level are you looking for? Tiamat is an actual deity, which means that she should be way, way beyond anything non-deific (save a sufficiently cheesy Epic caster). If you’re using Tiamat as your point of reference and you want this critter to also be a deity, you can use the rules in Deities & Demigods to build it, or you can also just plain not bother too much with the stats, because statting deities is often frankly pretty stupid. (If the deity’s stats—remembering that there’s more to “stats” than your six ability scores—are underbalanced, they don’t feel especially deific. If they’re sufficiently godlike that no mortal has a chance, why bother statting them at all, rather than simply saying that the god is untouchable by mortal means or can only be addressed with plot magic rather than with straight optimization?)

If you want this monster to be less of a god and more of a monster, then find something of an appropriate CR (hopefully something that’s been CR’d appropriately, which isn’t a guarantee in this edition) and use those stats as your starting point. Probably an appropriately high-level dragon. True dragons within a given CR bracket have a level of variation in their ability scores and special abilities, but they tend to be close enough together that you’ll have some idea of what a “normal” dragon of a given CR is likely to have. If you want this thing to be unique and powerful, you can then increase the numbers from the starting point a little bit, but remember that making something more powerful should really increase its CR, so if you make something noticeably stronger than the critter you used as a starting point, your result should have a higher CR than your starting point. (You can technically apply half-dragon to a dragon, even multiple times, but just brute-force repeated template stacking is kind of a surefire ticket to Crazytown.)

[Telonius]

The Wizards Archives have a Multiheaded template (http://archive.wizards.com/default.asp?x=dnd/mm/20020621a); you might check that out to see if it would give you what you're looking for.

[Crow_Nightfeath]

Yeah, I wasn't thinking diety or god level, I took the idea of different kinds of dragons as each head. And I've thought about just doing half dragon 7 times.. which does create a crazy powerful monster, but it doesn't actually give me what I want. I'm not entirely sure how powerful I want this creature to be CR wise. I know that the thing will at least have a CR of 26 (highest CR head)

[Uncle Pine]

First of all determine what colour you want for your dragon. Then, choose the dragon age and therefore size (minimum Huge if you want 8 heads) and base CR. Then add 14 to that number. Then another 4. Then another 8.

For example:
An old shadow dragon is a CR 17 Huge dragon with 25 HD.
A half-radiant, half-time, half-forest, half-sky, half-sea, half-underworld, half-vortex old shadow dragon is (allegedly) a CR 31 creature with one head and 8 different breath weapons. It still has 25 HD. Each application of the half-dragon template adds +2 CR.
An 8-headed half-radiant, half-time, half-forest, half-sky, half-sea, half-underworld, half-vortex old shadow dragon is (allegedly) a CR 43 creature with 8 heads, 8 different breath weapons and 39 HD. Adding 7 heads via the multi-headed template adds +4 CR, plus another +1 for each "head-based special attack of the original creature".

You can toy around and see which of the 8 base dragons has the best HD:CR ratio, but regardless of that your giant monster will likely be pitifully frail for its CR, even accounting for the +28 Con bonus it would get from its various templates.