I am afraid trigger will be involved, but this time you do not need spirit link from warcraft, you do it yourself
2 variables needed
spiritlinkcaster, spiritlinktarget
trigger:takes damage
event :
condition:
actions: -comment: this is simple, you refer triggering unit as the unit that takes damage, notice the event if empty, the trigger: linking will add the unit into this trigger using the add event function, watch below
trigger: linking
event when unit starts the effect of an ability
ability being cast equals spirit link
set spiritlinktarget = target of ability cast
set spiritlinkcaster = casting unit
add to trigger takes damage with {when spiritlinktarget takes damage}(this is unit specific trigger event)
add to trigger takes damage with {when spiritlinkcaster takes damage}(this is unit specific trigger event)
you can choose which one to add
now at the takes damage trigger, you can do whatever you want, e.g, when spiritcaster takes damage, you can actually get the damage taken using, Event response - damage taken (real type)... So I suppose you want to deal the damage taken back to the target... so the action will be, cause spiritcaster to deal spirittarget with Event Response - Damage Taken of type spells and normal
thats it you are done with the spirit linking thing, good luck for more advance abilities dude, if you want it by %, just simply do a 10/100 times damage taken that sort of thing
