8/22 Update (v0.3)
See the new post
8/14 Update (v0.2)
After a slew of great feedback from readers I’ve gone ahead and updated the file to v0.2. Check out the changelog inside for all of the changes!
v0.2: Download or Google Sheets Version
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Monster Creator Tool v0.1
Let’s start with the good stuff. You can download the first version of my excel based Monster Creator tool for FREE here: Download or Google Sheets Version
What is it?
A (hopefully) easy way to create monsters that adhere to the rules outlined in the Dungeon Master’s Guide as well as some common rules of thumb.
So where did this come from?
Having explored a number of the pre-written Forgotten Realms campaigns I’ve recently started work on a homebrew campaign (with more to come on that soon!). Once I started digging into the work though I ran into what I think is a pretty common challenge for many DMs.
When creating monsters I started, as most do, by playing around with existing stat blocks and just changing things here and there – this zombie is now a fire zombie and is immune to fire and can cast fireball because why the heck not.
However, I really wanted to dive into the mechanics behind monster creation and found that creating a monster that is balanced and adheres to all of the written rules was a lot more difficult than I expected! How bad could it be you ask? This post by The Angry GM does a better job than I ever could of summarizing all of the different factors to keep in mind during the process. Even most of the popular toolsets like D&D Beyond expect the user to make sure everything lines up correctly.
Knowing that I’d likely be creating quite a few custom monsters for this new campaign I decided to set myself up for success by creating a tool to allow me to create rules consistent monsters with ease.
I hope you enjoy the tool. This is just the first iteration though so please let me know if you have any suggestions or find any errors and go create something to terrify your players!
IndieRex 
Hello, friend!
Very useful resource–I’ve been working on my own sheet, and it’s really cool to see how we’ve approached them. You seem to have more of an emphasis on monsters using existing weapons; mine focused almost exclusively on what would be labeled “Custom” weapons on your sheet. Because of this, I noticed that your “Custom” weapons still try to scale the number of damage dice based on creature size. However, if you look at, for example, an Adult Black Dragon’s statblock, the bite, claw, and tail attacks deal 2d10, 2d6, and 2d8 damage respectively. So, while your “Custom” selection works well for an actual custom weapon, it doesn’t let me enter the correct damage statistics for the existing dragon’s natural weapons (it defaults to 3dX, because it is a “Huge” creature.)
Also, in the “Attack Reference” section, B106:D106, you ask for the “Type of saving throw required” which is not how Save DCs are determined. They are based off of the monster’s “spell/effect” ability modifier. To again reference the Adult Black Dragon, it’s breath weapon is a DC 18 Dexterity saving throw. However, calculating the DC with the dragon’s own Dexterity score would give you a DC of 15 (8+5+2). Instead, you should ask for the spell/effect’s ability modifier. In the case of a dragon’s breath weapon, they use their Constitution to determine the DC, despite requiring a Dex save from the target.
Otherwise, there’s a few aesthetic recommendations: I think cell C32 should be grey, I don’t know why B77 is labeled “Skill Perception Proficiency” instead of “Skill Proficiency,” I think you should enter the monster’s ability scores (determine Dex mod) before the AC section, etc.
Regardless, I hope these help. You’ve made a terrific resource and I don’t mean for my post to come across as all critiques–The sheet is impressive and I thank you for it. I’m looking forward to future versions. Feel free to email me if you want to be collaborative, I really like your work.
Thank you so much! Really appreciate the insightful comments and will work to address the issues you raised
So, on v0.2, you’re getting a Circular Reference issue on anything asking for a proficiency bonus. In cell C58, you have it look up the proficiency bonus based on the calculated CR. This would be fine so long as proficiency never affects CR, however, it does when calculating AC (Affects saving throws>Affects Effective Defensive CR>Affects overall CR.)
This is why the Monster Manual suggests that the Homebrewer sets an “Expected CR” to determine proficiency bonus. This way, it won’t affect CR and try to redefine itself.
For instance, try setting the cell referenced in C13 to C57 (manually entered CR) instead of C58 (calculated CR).