Aranya Red Elk

Trampling Charge.  If the elk moves at least 20 feet straight toward a target and then hits/rams a target with an antler attack on the same turn, if the target is a creature, it must succeed on a DC 14 Strength saving throw or be knocked prone. If the target is prone, the elk can make another attack with its hooves against it as a bonus action.

Sure-Footed. The elk has advantage on Strength and Dexterity saving throws made against effects that would knock it prone.

Skittish. If the elk is surprised (i.e. enemies get a surprise round), it becomes frightened for 1 minute or until its rider, if it has one, uses an action to calm it. If its rider gains the frightened condition it also gains the frightened condition and remains so until the rider becomes unfrightened and uses an action to calm it.

As it runs while frightened, it will move through any creature (enemies and allies alike) in its way, dealing 1d4 bludgeoning damage to a creature or object for each 5ft of movement (up to 2d4 damage). It ignores difficult terrain, but still suffers damage if it runs through an effect that causes it, i.e. Spike Growth.

An ally can attempt to hold it in place by succeeding on a DC 14 STR (athletics) check. If the elk has charged 20' or more, this check is with disadvantage. OR an ally can make a DC 12 DEX (acrobatics) check to avoid damage by diving to an adjacent square not in the elk's path, but becoming prone.

If held in place, an ally can also attempt a DC 13 WIS (animal handling) check, if the animal was frightened by a surprise attack. If the animal was frightened by a spell or similar effect, the DC is equal to that of what caused it to be frightened. The animal handling check can not be made if the fear is due to the rider being frightened. This check can be made with advantage if the ally is proficient in Animal Handling.

Antlers. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) piercing damage.

Hooves. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 9 (2d4 + 4) bludgeoning damage.