I'm a believer in teaching to fish : ). I've saved you most of the searching. How these pieces fit together is something you need to work out.
I will tell you roughly what you need though.
1 Target Skill
1 CONSUME Status (I recommend not giving this an Icon, you don't want the status visible as it only serves as a hook into your script)
1 Potion Entry (likely almost completely empty, only needed due to status requirement) (I recommend not giving this an Icon either as the Status will fallback to it if it exists
And then in Osiris, you need CharacterStatusApplied. Since you can configure the Target Skill to ignore anything without SP and you can configure the CONSUME status to ignore armor or magic armor, you can safely assume that if your status is applied, you can modify SP.
I would then try just using CharacterAddSourcePoints and see if a negative number works here. If it does, StatusApplied gives you both the caster and the target, so you add -1 to the target and +1 to the caster.
This is pretty much 85% of the ability. The rest is just making it, putting it together, and testing it.
Do note that it's possible the -1 approach will not work. If that happens, you might be out of luck unless you want a hacky solution like setting magic armor to 0 on skill cast and restoring it later.