Bone Prision

Roll an Intelligence d20 with a minimum of 14. 

If success then if an Skeleton type undead is at least at a distance of 30 ft of the enemy, that undead dies and it bones trap the objetive.

During this time the prision has an HP of 8 (at tiny size of the skeleton type) adding +10 for every size from tiny to gargantuan.

The enemy trapped has it's dexterity reduced by half of it's normal dexterity modifier. (example: if the normal DEX is 8, while trapped is 4).

It also does 3d8 of bludgeoning damage every turn ading + 1d6 for every size from tiny to gargantuan. (the same rule as it's HP)

If fail then the sekeleton dies and nothing else happens.