A player in the new campaign I am DMing wants their character, a halfling wizard, to ride around on a small bird, going for a Sir Didymus from Labyrinth feel. He suggested this could be his familiar, though he was very clear he doesn't expect this give him any special advantages (increased speed, flight etc.) beyond those a familiar normally grants. I liked the idea, so I came up with the following creature which would be added to the list of animal forms for the find familiar spell:
Bococho (riding familiar)
Small fey, unaligned
AC 12
HP 3 (1d6)
Speed 25 ft. (cannot fly)
STR 7 (-2) DEX 15 (+2) CON 10 (+0)
INT 2 (-4) WIS 14 (+2) CHA 7 (-2)
Skills: Perception +4
Senses: Passive Perception 14
Magical Mount. A bococho can carry its master (including their belongings), as long as they are of size Small or smaller. It won’t carry anything else.
Actions:
Peck. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) piercing damage.
It's based on the eagle's stats (since that's a Small-sized bird which is still CR 0), but with no flying speed (it's flightless), a better walking speed (matching a halfling's normal speed), no Keen Sight trait, and the new Magical Mount trait allowing it to carry its master and for simplicity's sake to magically ignore how much gear they're carrying. (For reference, the slightly increased Strength of 7 means it can carry up to 105 pounds, which seems pretty reasonable for carrying a halfling wizard, who will only weigh around 40 pounds plus gear.) It retains the eagle's hit points and (slightly tweaked for theme) attack.
Is this balanced? I'm pretty sure that the hp and attack won't be an issue, since it still has a tiny number of hp and it can't attack in normal circumstances anyway, but have I made it too weak removing it's ability to fly at all (rather than just specifying it cannot fly while being ridden, say) and removing it's sharp sight feature (advantage on Wisdom (Perception) checks involving sight)? Are there any drawbacks or advantages to this familiar that I haven't considered?
Best Answer
It breaks some rules, but should be fine
You are breaking some things that D&D tries to enforce:
However, while your familiar breaks those "rules", it looks fairly harmless. A familiar can't attack, so Peck is entirely irrelevant. Its high perception might cause some problems, but that is something other familiars can do as well, and its inability to fly makes it less viable for scouting.
The only real problem I see is that your wizard would be able to have the mount dash to double his normal movement speed every turn. How gamebreaking this ends up being depends a lot on how often you simply sneeze on the bird in round one to kill it.
For people who claim that this isn't really a problem because you can compare it to a 8 GP mule, there are a few key differences:
How important those two points are depends entirely on how your campaign. For some campaigns this would make no difference at all, for others where mounts die constantly, this could be a huge boon.