Magic Resistance. The Dwarven Sphere has advantage on saving throws against spells and other magical effects.

Immutable Form. The Dwarven Sphere is immune to any effects that would alter it's form.

Pack Tactics. The Dwarven Sphere has advantage on attack rolls if at least one of its allies is within 5 ft of the target and isn't incapacitated.

Custom Loot. When looted after being defeated the DM rolls 1d10. If the DM rolls a 10 the sphere has a Dwarven heavy crossbow. This crossbow is a +2 weapon.

Multiattack. The Dwarven Sphere makes two armblade attacks or two heavy crossbow attacks

Armblade. Melee Weapon Attack: +6 to hit, reach 5 ft., 1 target. Hit: 8 (2d12 + 2) [slashing] damage. 

Heavy Crossbow. Ranged Weapon Attack: +9 to hit, range 100/400 ft., 1 target. Hit: 10 (1d10+5) [piercing] damage. 

Roll Up. As a bonus action the Dwarven Sphere may enter ball Form, it may leave ball form as a bonus action. When in ball form the Dwarven Sphere’s AC is 20 and it's speed is doubled. If it leaves ball form within 5 feet of an enemy it incurs an attack of opportunity.