Just added your mod to the modpack I'm playing around with and this happened on startup. Figuring it's because both mods add variants to the frog mob. I have no clue if this is something that can even be circumvented from either mod, just thought I'd post it here in case it's something that can be fixed. :]
latest.log

Both Mods?
Which one is the other Mod, if that Mod has a github I can look into it. I added the variants in a very nondestructive way, meaning it shouldnt be a problem for any other Mods, but I have to look into it to be sure.

Both mods I'm referring to is SwampierSwamps and More Frogs, here's their curseforge page https://www.curseforge.com/minecraft/mc-mods/more-frogs-fabric, it seems they do have a github, if nothing can be done on your end I'll gladly forward it to theirs.

Well that is a good thing, it means we have found our compatibility issue!

Are you certain its a conflict between these 2 Mods? Just making sure, if it is it may or may not be an issue on my end. Does it launch when you remove More Frogs?
Them not being open source does make it a bit harder...

Unfortunately yes, I tested running the game with both mods installed together and separately, and in all instances it crashed only when both were installed together.

Sure thing!

Can you open an issue on their end, and link back to this one.
I think at this point the best thing to do is have the Mod authors (me and them) talk about this!

So update, I talked with the More Frogs Dev and they said they will fix the issue soon.
I will close this issue once the problem has been resolved!

The More Frogs Dev has announced that this issue has been resolved in the forge 1.1.1 release.