Use the abilities that come with 5th Editiondon’t try to reinvent the wheel, especially when it comes to things that affect the creature’s combat abilities.Crafting new combat tricks makes determining the Challenge Rating (CR) of the thing difficult to do, and thus makes your life harder when trying to create balanced encounters. Use What the Game Gives YouWhile making up your own abilities might be fun, keeping an even keel is important. If it’s a cat-like fey, give it advantage on Acrobatic checks.Even if those abilities don’t come up, it will inform your roleplaying of these new creatures.

Give them cool ribbon effects, which is to say, abilities that don’t come into play in combat.If you’re making a rat demon, give it the ability to squeeze through spaces smaller than itself, and the ability to speak with small rodents.

Play with damage resistancesall of that stuff. If something slithers, make it immune to being prone.Shake up the spell list, giving it a theme. Let the Flavor Show in the MechanicsThis can be done in subtle ways. What does it have to do that another creature can’t be reskinned to do? Once you know that, you can figure out how to put it all together. Firsr find whatever it is that you want, and distill that down to its core. Do you need a lower level Celestial, a higher level Fey, or a beast for your player to polymorph into once they’ve reached a level where the conventional beasts have topped out?These are all valid creations that the official D&D products lack.

Find the Flavor FirstFigure out what reason is leading you to create something new. Tweak it by describing it as some sort of twisted beast, say that its webbing is instead viscera, and there you go.My players never figured out they were fighting an Ettercap, they thought it was something completely new.

Animated Armor Medium construct, unaligned Armor Class.

5e monster stat block creator