Giant goat
From Ardrana
Giant goats are reclusive herbivores that dwell in hilly country. They are semi-intelligent and stand 5 feet or more at the shoulder. They will aggressively defend themselves against any threat, butting with two sharp horns. In rare cases, these animals have been tamed as steeds.
Note: Giant goats originally appeared in this form in the 2nd Edition Monstrous Manual for the AD&D game from TSR. Their use here is for the purposes of providing context for the campaign only.