Illusion Affinity. The guard is immune to the effects of any spells from the school of illusion.

Barbed Weaponry. When a creature fails its Dexterity saving throw against Barb Blast by 5 or more, or if the total of the attack roll for Barbed Spear exceeds the target's AC by 5 or more, a thorn is stuck in the target. This thorn deals 1 piercing damage to the target whenever it uses an action or moves more than half its speed in a turn. The target or any creature within 5 ft. of the target can use an action to remove the thorn. 

Barbed Spear. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) piercing damage, or 5 (1d8 + 1) piercing damage if used with two hands. 

Barb Blast. The guard shoots a cluster of barbed thorns at a space it can see within 30 ft. Any creatures within 5 ft. of that space must succeed on a DC 11 Dexterity saving throw or take 1d6 piercing damage.