Compared to the other PHB races, where does Mousemen homebrew race stand, in terms of balance?

Question

Short story, we are trying to port mouse-guard characters into a dnd-5e game. There is no official mouse/rat humanoid race, so we are going to homebrew it.

Googling around, I've found this reddit post and this on the dndwiki. But none of them felt right for us, so we decided to bake our own.

Mousemen

Ability Score: Dexterity +2

Age: Mousemen become adults at the age of 8 years old, and can live about 75 years.

Alignment: Mousemen are mostly good because of their strong sense of community and mutual cooperation.

Size: They small size, between 2 and 2 1/2 feet tall when standing erect on the rear paws.

Speed: Mousemen basic walking speed is 25ft. If they have both hands free, and are not wearing heavy armor, they can scurry on all four paws for a speed of 40ft

Darkvision: They can see in dim light within 60 feet as if it were bright light, and in darkness as if it were dim light. They can't discern color in darkness, only shades of gray.

Nimbleness: Mousemen can move through the space occupied by creatures at least one size larger than them.

Keen Senses: Mousemen are proficient with the perception skill. They have advantage on tests based on smell, and can identify individuals they met before by their scent if they are within 20 feet.

Vermin Resilience: Mousemen have advantage on saving throws against disease, and all effects of disease on them is halved, including damage.

Subrace: you can choose between Heartwood mice, Woodland mice and City mice

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Heartwood Mice form villages on the outskirts of rural settlements and are the smallest subrace of Mousemen. They are expert with farming and crafts.

Ability Score: Wisdom +1

Squirm: When wearing light or no armor, they can move through any space a tiny creature can pass.

Artisan Tools: You gain proficiency with 1 artisan tool of your choice.

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Woodland mice: living in wild untouched forests, these rugged mice are often distrustful of outsiders, but have learned to rely on other animals.

Ability Score: Constitution +1

Speak with beasts: Woodland mousemen can communicate simple ideas with beasts of small size or smaller (regarding outsiders, predators, dangers, food, water, shelter). Those beasts are also unusually friendly with the woodland mousemen.

Animal Handling: Woodland mousemen have an innate knack with animals. They are proficient in animal handling.

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City Mice form their own cities in hard to reach places, or make their own enclave in the sewers or slums of bigger species' towns. They have a chivalrous mindset, and work to the benefit of their community. City mice are often lawful. Flamboyant and sharp-tongued, they often talk themselves out of danger.

Ability Score: Charisma +1

Weapon Proficiencies: All city mice are proficient with rapier, shortsword, dagger and shortbows.

Skill Proficiencies: City mice are proficient with persuasion.

We also applied this ballpoint racial trait breakdown

and came up with this summary:

Ability +2
Size -1
Speed: +0.5
Darkvision + 0.5
Nimble + 0.5
Senses +1
Resilience: +0.5

Subraces All of them: Ability Score: +1 Proficiency: +0.5

Heartwood - Squirm: +0.5

Woodland - Speak with beasts: +0.5

City - Weapon proficiencies: +0.5

This gives the race as a whole a 6 score.

Answer 1

I'll start saying that yes, it's balanced overall, but might be weaker in combat than other races.

The only combat-relevant feature I see is the resilience against diseases.

Let us compare with other races, focusing in combat features. I'll ignore the +2/+1 ASI, as this is default for everyone. This means I'm considering your race having a +0.5 score in combat. I know speed and darkvision have some influence in combat, as well as keen senses in terms of not being surprised or surprising the enemies, but I mean from a DPR/Tankyness combat sense, or things that directly influence saving throws, attack rolls and damage.

Gnomes

Advantage against Wis, Cha and Int magic is certainly stronger than resilience against diseases. I don't think I need to argue much about it - the guide itself gives a 2 score for the Gnome.

Half-Elf

Half-elves get +1 ASI, which is a +1 score for combat. They also get Fey Ancestry, which is arguably as useful as your resilience in combat, meaning their +1 ASI is the major difference.

Half-Orcs

Relentless Endurance and Extra Crit give them +1.5 score in combat, against your +0.5.

Tiefling

Fire Resistance and Infernal Legacy again give a +2 in combat.

Dragonborn

They have the worse score in the guide, but their damage resistance is certainly more meaningful than yours, in average campaign scenarios, and Breath Weapon has its situational uses.

Halfling

Lucky by itself should be as useful as the resilience. Lightfoot has Naturally Stealth, which pretty much nullifies the -1 from size (which I already think is overestimating how bad it is to not be able to use heavy weapons or -5ft) and Stout has Poison Resilience. Both also have advantage against Frightened.

Elves and Dwarves

Both already have greater scores than other races (7+), but again, both have more combat-focused features (either +1 ASI, +1 HP/level, cantrips...)

Human

Let's be fair, normal human is a bad race. Even if the guide gives a 6 total score because it gives +6 ASI, hardly any class is actually using these to their full potential. Your race is better than normal humans, but I'd say any race is.

Variant Human

On the other hand, Variant Human might be the strongest race in the game, depending on the setting (mainly how much not having Darkvision will hurt them), since we have some strong feats. It's hard to compare since it depends on the feat chosen, but I'll argue that Sharpshooter beats +1 ASI and Resilience against diseases combat-wise.

All of this is just to say: compared to other races, you might be lacking a combat-focused feature.

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Notes on the Ability Scores given and classes likely to use this race

Similar to how Normal Human is considered a bad race because +6 ASI doesn't mean much when there's no class or role that will use each score, let us quickly review your Ability Scores to see if they are indeed worth the +3 Score.

Heartwood

+2 Dex/+1 Wis: Ok, this is similar to Wood Elf, it's certainly useful for Ranger, maybe Druids. I do think Wood Elf is slightly better choice for both, balance-wise, than your Heartwood, but not enough to make it a "not a choice" scenario. (i.e. I think this is already balanced enough, but you could give an extra .5 feature to make it a more fair choice)

Woodland

+2 Dex/+1 Con: Certainly useful as well. Con is pretty much a secondary stat for every class. Dex Fighters or Rogues can make use of this stat distribution. I would say that, similar to Halflings, this would be taken mostly by Rogues.

I think the comparison between Stout Halfling and Woodland Mice depends on how strong will Darkvision actually be, compared to Lucky.

City

+2 Dex/+1 Cha: Again, similar to (Lightfoot) Halfling, so we would expect it being chosen by Rogues. Bards and Sorcerers can also benefit from it.

I think that, similar to Wood Elf x Heartwood, Lightfoot Halfling is stronger, mainly due to Naturally Stealth and Lucky, but not enough to completely dismiss your mice as a choice. Again, Darkvision being more relevant than usual can make your race get closer as well.

Conclusions

Your race is not "too weak", but I think it is slightly weaker, mainly for combat purposes, than the existing ones. You could certainly give an extra .5 score feature without making it overpowered. As a suggestion, some kind of Hiding feature, similar to Naturally Stealth and Mask of the Wild, preferably weaker than Naturally Stealth though.

As a side note, I really like the flavor in every feature you put there, and I would certainly pick it as a race for a PC of mine , even if it's suboptimal.