Maybe a cerberus?

http://www.furaffinity.net/view/24384168/

Maybe my own dragon or Kion's Ginubis fit the bill?

It'd be cool to see a Xenomorph.

Otherwise this demon, Ragnarøk, could fit the bill:
https://www.furaffinity.net/view/19877994/
https://www.furaffinity.net/view/19877970/

Stygian Zinogre (Monster hunter @Campom)?

I second this. Basically a badass demonic dog dragon. The naturally large chest on them are prime reasons to beef em up. http://monsterhunter.wikia.com/wiki.....tygian_Zinogre for reference.

An FFX Behemoth?

Third

Perhaps Shogoth from Defenders of the Earth? He could always us more exposure and huge muscles:

http://www.furaffinity.net/view/9483150/

http://www.furaffinity.net/view/5399749/

Maybe a minotaur?

Yes ! Second that ! LiKe Manny Taur from Monster High

Can't say I'm familiar with that character.

Also, is Monster High a spin-off cartoon based on Monsters University?

The typical super sexy Incubus ~

Welll one combination of 2 species? Like drashark? (Dragon + shark)

Behemoths, DOOM demons... I dont know too many, but some of the Monster Hunter series's monsters would be cool.

Well, if you're looking for demons, I do have some ideas.
http://megamitensei.wikia.com/wiki/Pazuzu
http://megamitensei.wikia.com/wiki/King_Frost
http://megamitensei.wikia.com/wiki/Gagyson
http://megamitensei.wikia.com/wiki/Orobas

Definitely a behemoth or maybe a werewolf?

what about a hellhound?

Chaor from Chaotic~

https://vignette3.wikia.nocookie.ne.....20110218145153

A bunyip.

Working on a werewolf design that'd be perfect for this.

More Bowser.

A clay demon? :3
https://www.dropbox.com/s/dg7vgp27g.....demon.jpg?dl=0

Or gargoyles? owo
https://www.dropbox.com/s/95jhdoavy.....goyle.jpg?dl=0

Would definitely say hellhound.

Pretty much any demon from doom 2016 >.>

Diablo and Duriel from the Diablo series would be good choices for Demons, and probably many other demons from that series of games!

How about a Chimera or a Manticore?

An Astral Dreadnought from Dungeons and Dragons would be fun.

http://78.media.tumblr.com/715d3208.....1VN1r0zz7o.jpg
https://i.pinimg.com/564x/46/1c/c7/.....ure-astral.jpg

A minotaur perhaps.

A nightmare (ya know, giant black horsey with a mane of flame)

Perhaps a Roc or some other kind of demonic bird. (The three eyed raven from Game of Thrones?)

A chimera of whatever fancy configuration.

A gryphon.

A basilisk? (The snakey variant ala Harry Potter, rather than the chicken)

Really, I could keep going with suggestions.

Kitsune don't often get the huge muscle treatment...

Narga!
The world needs more Nargacuga~

Beastly gnoll guy?

Brachydios or a Zinogre the Monster Hunter series, always need more buff monsters in the world

As a demon and a behemoth I'm going to bereally biased and say behemoths, and butcher from Diablo

Nessie? Or make a male version. Call him Nestor?

Would love to see you try Jörmungandr, also know as the World Serpent, from Norse mythology

A Troll, Ogre, or Orc for monstermen
and how about a typical hprned demon with goat legs on the demon side

Fallout Deathclaw please

I think there are already lots of other great things here, especially would like to second/third the things about Incubus and Hellhound/Cerberus.

But since I really like exotic/rare monsters that are often underrepresented, I want to try to suggest a few in case one catches your fancy despite being only mentioned once:
Spiky Rats/Gophers
Werebadgers (those particularly are kinda gaining a bit of popularity these days as something specific)
Dwarves (those aren't done as buff monsters nearly often enough but I feel like they are a good choice for it, and my world has several Dwarf-like monsters, all of which tend to be buff fairly often, at least among generics, so I know it can be done even though it isn't done often)
Greator Imps (not all Imps are tiny, nor should they be... though I suppose larger ones might look similar to other monsters like Oni...but those aren't mentioned often either...)

Okay, maybe that had too many words, but I felt like explaining my...unconventional suggestions, to maybe give them a bit of credibility.

Either Gym - Demons or Gods workout space.

Hi! :) I'm not asking you to draw any of these characters (unless you really want to), but I would like to link you to some of my more "monstrous" characters for potential gym-tastic inspiration!

Eldrikke - Western Bodybuilder Dragon - http://www.furaffinity.net/gallery/.....0497/Eldrikke/
Mora - Demon - http://www.furaffinity.net/gallery/.....der/50498/Mora
Garon Rex - T-Rex - http://www.furaffinity.net/gallery/.....0495/Garon-Rex

Again, hope this helps you with some ideas!

A little late but how about this guy - https://orig00.deviantart.net/0868/.....on-d6gpt87.jpg

Perhaps my Cerberus