Thanks for the answer, Ishara. I had already found a way when you posted your message though. When I ticked "Detrimental" box in Magic Effect, my burden spell became harmful. Created a "self" version of the spell and tried that on my character and it worked perfectly. But I think negative CarryWeight values are ineffective against NPCs because when I use my custom spells or click on an NPC and type "set.carryweight -1000", nothing seems to change. NPCs does not slow down like player character. Is this engine-related or is there a solution for this?