Thank you for taking the time to read through this guide. Ultimate Chimera Hunt is a gamemode developed by Aska and Fluxmage. More information on the gamemode itself follows in the sections below.
The two main UCH addons as of the time of writing as as follows:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=685997425&searchtext=Ultimate+Chimera
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=385438672&searchtext=Ultimate+Chimera

The goal of the Pigmask Army in the gamemode is to press the button on the back of the Ultimate Chimera in order to switch it off and win the round. How challenging this is depends on how good or bad the players are. The Pigmasks can use Shift to dash, which depletes their dash meter, although it regenerates over time. Once Shift is clicked the Pigmasks dash meter will continue to deplete even if Shift is let go of or the Pigmask doesn't move, so should be used only when needed. Left clicking as a Pigmask is used to press the button on the Chimera, and for not much else. Right clicking makes the Pigmask salute, with no other effect.
Pigmasks can use F for their flashlight, and can jump and crouch using the ordinary Gmod control scheme. Each time an individual Pigmask presses the Chimera's button they go up in rank. There are 4 ranks in all: Pigmask (default), Pigmask Captain, Pigmask Major and Pigmask Colonel. The higher ranks (Captain, Major, etc.) have the effect of having longer sprint times and losing fear easier when the Chimera uses its roar attack. Of course, they also look cool and show other players how skilled you are at Ultimate Chimera Hunt.
The image above shows all ranks. The pink Pigmask is default, blue is Captain, green is Major and grey is Colonel. The guns shown in the image are not part of the game (they're from TF2), and this image was actually made using ragdolls for the Pigmasks, but for the purposes of this guide it shows all the different Pigmask ranks.

Information on the abilities of the higher Pigmask ranks was provided by Deaconator and Riolu, thanks guys!

This concludes the Pigmask section, although more information may be added should the need arise.

As the Ultimate Chimera your goal is simple. Kill all of the Pigmask Army and avoid getting your button pressed. To do this the Chimera has an arsenal of abilities. Simple left clicking will make the Chimera bite, a powerful move which kills any Pigmask unlucky enough to be in its jaws. Right clicking makes the Chimera roar, which scares nearby Pigmasks into automatically running, depleting their run meters and making them vulnerable after their meters are depleted.The image above shows the Chimera's roar, dash and tailwhips meters. The Chimera can whip with its tail using R, throwing Pigmasks trying to get at the button a short distance. Repeatedly jumping as the Chimera allows it to fly with its wings, but depletes its dash meter. The Chimera can dash and stop as it pleases just by letting go of Shift. The Chimera can see in dark places with its night vision, activated by pressing F on the keyboard.

This covers the abilities of the Ultimate Chimera. If you think I should add some more information, please comment so I know what to add.

Should a Pigmask die, they become a ghost, invisible to any players still alive, although ghosts can see other ghosts. The ghosts can fly by holding Spacebar, but otherwise becoming a ghost is just a way to pass the time until the end of the round.
There are two kinds of ghost, Fancy Ghosties and Ghosties.They have no real differences other than that Fancy Ghosties carry a glass of wine, as shown above. Whether you become a Ghostie or Fancy Ghostie upon death is by random chance.

This gamemode is all about teamwork. If Pigmasks all tackle the Chimera by themselves it's highly likely they'll end up getting munched on. Players should try to distract the Chimera so that others can get at the button, and sometimes taking one for the team can be a good thing. Pigmasks should also try to look for the best opportunity by trying to flank the Chimera, catch it by suprise or go for the button in a period of vulnerability, such as immediately after it has done a biting attack, as there is a tiny window for running around it and at its button before it can bite again. Miss an opportunity however and you might be dead pork.
The Chimera should always remain aware of its surroundings and make sure it does not get snuck up on. If a Pigmask is right by the Chimera's button a tail swipe is of course a good idea, and if the Chimera is getting swarmed by loads of Pigmasks then a good roar ought to scatter a bunch of them. The Chimera should dash when chasing vulnerable Pigmasks, but otherwise dashing isn't too neccesary. Camping is frowned upon, as in many games, and a good Chimera should never have to stand with its button facing some wall where no Pigmasks can possibly reach.

A tip from Man of Shadows, if a player is camping as the Chimera, you can crouch-jump over their heads and press the button, if they don't see it coming and stop you. Thanks Man of Shadows!

If anyone has any other tips they'd like to contribute then please comment and I will try to add them in.

Ultimate Chimera Hunt is a unique and fun Gmod gamemode based off of the game MOTHER 3 (which is really good btw, I've played it), which was never officially released outside of Japan, although a fanmade translation of the game is available online. Sadly I find that there are very few good Ultimate Chimera Hunt servers which are well-populated, so it would be nice if more people decided to set up a UCH server. The gamemode can be found with one simple search on Steam Workshop. On Gmod Tower UCH if you press the Chimera's button 150 times you get an achievement and a pet Chimera! This information was provided by Rapitor Jedasus, so thanks to him for that.
I hope this guide has been helpful and informative and will make playing the Ultimate Chimera Hunt gamemode a fun experience for you. Again, if you have any advice or ideas which you think should be in this guide then please comment and I will put them in and give you credit.