Ugh, humanoid limits things. I know Slaanesh and Tzeentch both had non-humanoid daemonic beasts - some were mounts, some just attacked.
Here's my idea, if condition A is ever lifted:
Prince of the Forest
Domains: Elysium, Connection, Weaving, Earth[, any other terraforming-related domains we pick up, like Weather]
Princes of the Forest take the form of large deer or elk, with amber eyes, leafy or flowering branches in place of antlers, and fur usually in shades of green, though autumnal shades (brown, yellow, orange, red) are also known.
They can serve the faithful as mounts and command lesser lifeforms made with the Maiden's blessings, but their larger purpose is to anchor Her power to an area, transforming barren or hostile environments into peaceful paradises and making it easier to summon more of the Maiden's servants.
While great herds have occasionally been reported coordinating to terraform worlds, Princes of the Forest are usually found alone. If their enforcement of the Maiden's domain of Elysium can be overcome or worked around, or if they have not been present long enough for Elysium to take hold, then they can be slain to end their effect on the local environment - while they can attack with their antlers or hooves, they are no better at combat than any mundane cervid.