Bolster Skeleton

You channel necromantic energy to fortify the skeletons under your control. Choose any number of skeletons within 60 feet of you that are under your control. Each chosen skeleton gains a permanent increase of +2 to AC and +5 to its hit point maximum.

This increase is permanent and remains even if you lose control of the skeletons. Even though these effects can only be dispelled by dispel magic, this only works on a single skeleton at a time. This spell has no effect on skeletons already bolstered by this spell.