Brute. A melee weapon deals on extra die of its damage when the Undead Primipilus hits with it (included in the attack).

Trained Thrust. A one handed melee weapon gains 5 feet of reach when the Undead Primipilus attacks with it (included in the attack).

Martial Advantage. Once per turn, the Undead Primipilus can deal an extra 18 (4d8) damage to a creature it hits with a weapon attack if that creature is within 5 ft. of an ally of the undead champion that isn't incapacitated.

Skeleton.  If the Undead Primipilus leans closer to a skeleton it gains +10 feet of movement.

Zombie. If the Undead Primipilus leans closer to a Zombie it gains access to Undead Fortitude. 

Undead Fortitude. If damage reduces the Undead Primipilus to 0 hit points, it must make a Constitution saving throw with a DC of 5+the damage taken, unless the damage is radiant or from a critical hit. On a success, the Undead Primipilus drops to 1 hit point instead.

Multiattack. The Undead Primipilus makes three melee attacks or two ranged attacks. 

Spear. Melee or Ranged Weapon Attack: +9 to hit, reach 10 ft. and range 20/60 ft., one target. Hit: 13 (2d6 + 5) piercing damage, or 15 (2d8 + 6) piercing damage if used with two hands to make a melee attack.

Shield Bash. Melee Weapon Attack: +9 to hit, reach 5 ft., one creature. Hit: 11 (2d4 + 6) bludgeoning damage. If the target is a Medium or smaller creature, it must succeed on a DC 15 Strength saving throw or be knocked prone.

Leadership. (recharges after a short or long rest). For 1 minute, the warrior can utter a special command or warning whenever a nonhostile creature that it can see within 30 feet of him makes an attack roll or a saving throw. The creature can add a d4 to its roll provided it can hear and understand the undead champion. A creature can benefit from only one Leadership die at a time. This effect ends if the Undead Primipilus is incapacitate

Parry. The Undead Primipilus adds 4 to its AC against one melee attack that would hit it. To do so, the undead champion must see the attacker and be wielding a melee weapon.