Minor Ring of Primal Power (5e Equipment)
From D&D Wiki
Ring, rare (requires attunement)
Wind Sail. You can take on an altered form. A short sail protrudes from your spine, catching the wind and allowing you to move more quickly on all fours. You can take the Dash action as a bonus action in this state, however, you cannot attack while moving on all fours, save unarmed melee attacks utilizing your head. As the sail is a large and easy target, attacks against you are rolled with advantage. You can activate and deactivate this effect using a bonus action. Your armor must be altered for the sail beforehand or it will fail.