Byui'Ram

Seithr Form (Recharges After a Short or Long Rest). If the ram would be reduced to 20 hit points or fewer, the ram regains an amount of health to bring it to 65 hit points. The ram then gains access to Seithr Imbued Actions. Award a party an additional 500 XP (3,400 XP total) for defeating the ram after its Seithr Form activates.

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

Hard-Headed. The ram's attacks are treated as magical and adamantine for the purpose of bypassing resistance and immunity to nonmagical attacks. The ram cannot be stunned, incapacitated, knocked unconscious, and is immune to psychic damage.

Seriously, Watch Out. Creatures must immediately move out of the way when they succeed a Dexterity saving throw against any of the ram's area attacks. If a creature doesn't have enough movement speed to do so, they fail the saving throw. If the ram moves at least 20 feet straight toward a target and then hits it with any ram attack on the same turn, the target takes an extra 5 (2d4) bludgeoning damage.

Multiattack. The ram makes a Ram attack and a Slam attack.

Ram. Melee Weapon Attack: +9 to hit, reach 10 ft., 1 target. Hit: 12 (3d6 + 2) bludgeoning damage. Additionally, the ram causes one additional effect:

1. Stunning Ram. The target must succeed a DC 15 Constitution saving throw or be stunned until the end of their next turn.
2. Shoving Ram. The Ram can immediately shove the target up to 15 feet away and knock it prone.
3. Denting Ram. The Target has their AC reduced by 3 until the end of the ram's next turn.
4. Marking Ram. Every creature within 60 feet of the target is effected by the faerie fire spell (DC 15) until the end of the ram's next turn (no concentration required)

Slam. The ram leaps 10 feet upwards and slams into the ground, causing a magical burst of energy that varies in effect:

1. Forward Slam. All creatures in a 60-foot line that is 15 feet wide must make a DC 15 Dexterity saving throw. A creature takes 10 (3d6) force damage on a failed save or half as much damage on a successful one.
2. Burst Slam. All creatures in a 30-foot sphere must make a DC 15 Dexterity saving throw. A creature takes 10 (3d6) force damage and is pushed 10 feet away from the ram on a failed save. A creature takes half as much damage and isn't pushed on a successful one.
3. Trampling Slam. +14 to hit, one target within 5 feet of the ram. On a successful hit, a target is knocked prone, takes 18 (4d6 + 4) bludgeoning damage, and is restrained in the ground beneath them. A restrained creature can use their action to free themselves.
4. Barrier Slam. The ram casts the spell wall of stone 5 times (DC 15) and does not need to concentrate on the spells. The walls disappear at the end of the ram's next turn.

Disengage. The ram can disengage as a bonus action.

Opportunistic Headbutt. The ram can take an opportunity attack when a creature enters it's reach. Additionally, a creature that is hit by the ram's Opportunity Attack has their movement speed reduced to 0 for the rest of their turn.

If the ram's Seithr Form trait has activated in the last hour, it can use the options below as Seithr Imbued actions. The ram can take 3 seithr actions, choosing from the options below. Only one seithr action can be used at a time and only at the end of another creature's turn. The ram regains spent seithr actions at the start of its turn.

Telekick (Costs 1 Action). The Ram conjures a portal and kicks it. One creature within 60 feet of the ram must make a DC 15 Dexterity saving throw or take 5 (1d6+2) bludgeoning damage and be knocked prone.

Up and Down (Costs 2 Actions). The ram makes one Ram attack. On hit, the target takes no damage and is knocked 20 feet up into the air. The ram then teleports upwards and targets the thrown creature with a trampling slam attack.

Burnout ((Costs 3 Actions)1/day). The ram takes a course of actions.

1. The ram falls through two portals that it conjures- one in the ground, one in the air, building momentum. Both portals then disappear. 
2. A new portal appears facing a creature. The ram then runs out of that portal in a straight line, not provoking  opportunity attacks. All creatures in a line that is up to 100 feet long that is 15-feet wide must make a DC 15 Dexterity saving throw or take the damage of the ram attack + 5 additional bludgeoning damage. A creature that fails this saving throw is knocked prone and out of the area of the line. The ram then disappears through another portal. The Seithr action then ends.
3. New random portals appear at the end of every creature's turn and step 2 repeats until the ram's turn starts. The ram then loses it's action for that turn and cannot use it's movement speed as a wave of lethargy washes over it.