Burrowrider

Their enraged bellows are muffled by the dirt, but none can deny the impact a burrowrider has when they emerge onto the battlefield from below. Perhaps most frightening is that the greatest of these warriors are capable of driving their mounts through the very stone—making no place safe from these berserkers.

Small Only. The unusual demands of these archetypes require adventurers of Small size—the techniques are impossible without both a rider and a mount of diminutive stature. At the Narrator’s discretion a PC of Medium size may be able to select one of these archetypes (using a more suitable Large-sized beast that otherwise follows the requirements of Unusual Mount), but they are not intended for such adventurers.

Unusual Digging Mount

When you choose this archetype at 3rd level, you gain the Unusual Mount feature and become the mounted guardian of a dire mole or giant badger . You also gain proficiency in the Spirited Steed combat tradition. These maneuvers do not allow you to attack with your unusual mount, though you can use such maneuvers as normal on a different mount.

Raging Mount

Also at 3rd level, whenever you enter or end a rage, your unusual mount does as well. While raging, it receives the same benefits you do, including its own pool of rage hit points. However, while raging your unusual mount instead gains resistance to all types of damage. In addition, while you are riding your unusual mount and you both are raging, the DC to resist your Furious Critical features increases by 1.

Tunnel Control

Beginning at 6th level, by spending a bonus action to help carve along the way, you can choose whether your mount’s travel through the ground leaves a passageway. When making a passage, your unusual mount moves at half its normal burrowing speed and can’t take the Dash action, but leaves a stable, 5-foot diameter tunnel behind it. In addition, your eyes have become accustomed to the dark. You gain darkvision to 30 feet or extend your existing darkvision by that amount.

Dig Hard

At 10th level, your fury can spur your mount to great efforts. While you are both raging, at the start of your turn you can use your reaction to spend 1 exertion to make your mount better at digging, allowing it to burrow through unworked stone until the end of your next turn.

Unexpected Emergence

Also at 10th level, on any turn where you begin by emerging from the ground while riding your unusual mount, your melee weapon attacks score a critical hit on a roll of 18–20. Any further increases to the range of your critical hits increase your critical hit range while using this feature by 1 (maximum 17–20). In addition, on the turn that you emerge, you can use your reaction to choose one creature you can see within 10 feet. If the creature saw or heard you emerge, it must succeed on a Wisdom saving throw (DC equal to 8 + your proficiency bonus + your Charisma modifier) or be rattled until the end of your next turn. A creature that successfully resists this feature is immune to its effects for 24 hours.

Dig Harder

Starting at 14th level, nothing can stop your mount. While you are raging, at the start of your turn you can used your reaction to spend 2 exertion and enable your mount able to dig through anything, allowing it to burrow through any material until the end of your next turn. At the Narrator’s discretion, some natural material (such as adamantine) or magically reinforced material may be too hard to dig through.

Additionally, you can choose to instead inflict the frightened condition when a creature fails its save against your Unexpected Emergence.