The Emerald Mech

Regeneration.  The Emerald Mech regains 20 hit points at the start of its turn if it has at least 1 hit point. A mending cantrip heals it for 2d6 per turn of the spells casting.

Aura of the Mech: Creatures of its pilot's choice within 30ft of the mech gain a bonus of 1d4 on their attack rolls, damage and saving throws.

Piloted: The pilot's mental ability scores replaces the mech's, its strength and constitution scores are replaced by the pilot's charisma score, and it adds its proficiency bonus to its skills and saves that the pilot is proficient in.

Multiattack. The mech can attack with either Slam or Shoulder Ballistae as many times its pilot has attacks per turn, using any combination of the attacks.

Slam. Melee Weapon Attack: +(Strength Mod + Proficiency Bonus) to hit, reach 10ft., 1 target. Hit: 3d10 + Strength mod [force] damage plus 4 (1d8) radiant damage. 

Action Ranged Attack. Ranged Weapon Attack: +(Strength Mod + Proficiency Bonus) to hit, range 80/180 ft., 1 target. Hit: 3d8 + Strength Mod [radiant] damage.

Reaction Name. The mech can choose to redirect any attack or spell casted targeting its rider onto itself as a reaction.