Interesting... I like the core idea and core theme...
I kinda would rework it to something more like...
Spell Pull: "Targeting Spells can only target creature with this ability while it is in play."
Upgraded can gain Spell Shield: "damage from spell is reduced by half"
I am thinking where beside use to protect your or your creature, its main use is to use to suck up enemy buffs, like blessing or heal, etc. Of course, it act as a double edge sword, as it also mean you can not buff your other creature beside this one.
Retreat is good, but feel it make it tad too powerful.