Brunnis the Steady

Mobile Mountain. Brunnis the Steady is monstrously big. Not quite as tall as a Goliath, but certainly wider; not quite as broad as an ogre, but certainly denser (both physically and mentally). For all spells and abilities that affect a Medium or smaller creature, Brunnis is considered Large. 

Attack. Brunnis makes one Greatsword attack and Bouldering ahead 10 feet further.

Greatsword. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 10 (2d6 + 3) slashing damage.

Bouldering. Melee Slam Attack (special): All targets in path DC 8 [+1 per 10 feet] Dexterity save, taking full damage on a failed save and no damage on a successful save and can use a reaction to make an Opportunity attack (but Brunnis can swing his Greatsword at the first target to dodge him). Hit: 14 [+7 per 10 feet] (2d10 + 2 [+1d10 +1 per 10 feet]).

Brunnis the Steady starts running at a target and builds momentum. Each round, his speed increases by 10 feet. As his movement speed increases, so does the damage inflicted when he hits and the difficulty to dodge him. Brunnis can turn up to 90 degrees per 5 feet during this movement (e.g. on a battle map, move 1 square to the right, then 1 square to the right of that for a U-turn). 

***An enemy can choose to halt Brunnis's momentum by making a Strength save of the same DC as the Dexterity save to dodge. On a failed save, the target takes double damage and is knocked prone. On a successful save, Brunnis and the target both take half of Brunnis's Bouldering damage and Brunnis comes to an immediate halt.