[Advice Requested] Balancing an odd beast companion

[BinkyBonky]

So far we're figuring it'll be a useless baby/juvenile until I'm level three, and will do nothing (aside from probably misbehave).
Given that my character itself is somewhat handicapped being a half-drow (disadvantage in broad daylight) having it able to help me is a bonus since it can "see" better (echolocation). My saving grace will be casting faerie fire 1/day to negate some of the disadvantage. Definitely a strong dungeon crawler but outside I'm pretty nerfed, especially as a ranger.

We're thinking of adapting Tasha's rules for beasts with some modified stats to reflect the darkmantle. Darkness will be a 1/day cast for the darkmantle as well, so it'll help, but not always. I think the no breathing feature of its attack will not be applied (or not until later in levels?)

I'm not very familiar with how beasts level using tasha's rules, so I'm not entirely sure how well/poorly this guy is going to level. Not ever having a magical attack will put it at a disadvantage as we progress to more resistant enemies, but the fact that it assists me in my own attacks should probably be enough. It has a pretty low AC so I think (hope?) it will help keep it from being OP even as it levels. The fact that it can only attach to medium or smaller creatures also helps keep the blinding factor of its attack from being ridiculously overpowered.

I think basically we're hoping for it to kinda buff the somewhat weak build of a beast master ranger, and make for some interesting gameplay. A half-drow with a big ugly monster is certainly going to be a challenge in any city setting, as I don't think the npc's will take kindly to us.

Still brainstorming! This is going to be tricky, but I think it'll be fun.