possible underdark animal companions for revised ranger?

[that_one_kobold]

I will be in a group running Out of the Abyss very soon here, and I just so happen to be a forest gnome ranger. We will be starting at level 1, but I'm wondering what a good underdark themed animal companion might be. I believe that it must:

Have 15 hp or less

Do no more than 8 damage in a single attack

Be of medium size or less

My DM said he can allow me to just downsize a giant lizard, so that I can have a wall climbing sub-terrainian buddy! Any other great suggestions?

EDIT: I would also want it to be medium, because mountable pets are the best pets!

[RakiReborn]

You can find this in the DMG p305 (appandix A), which lists creatures per environment. If you look at the options there you can find out which beasts would fit your criteria.

[nickl_2000]

Giant Wolf Spider or Deep Rothe would be great choices

[xroads]

I've heard some rangers can use the pteranodon from Tomb of Annihilation. Perhaps you could reskin one as a giant bat (unless there already is stats for one somewhere)?

[ImproperJustice]

Those requirements are harsh since my first suggestion was going to be the Giant Poisonous Snake or Wolf Spider.

Lizard is good too.