Simply make a Damage + 5 Item Ability give it 100 levels. Then make a trigger
Event-
Generic Unit Is Attacked
Condition-
Boolen Attacking unit has buff (YourBuff) = to true
Actions
Unit- Increase level of ability (ItemDamage+5) for (attacking unit)
Or something like that oh and make a trigger on the cast of the ability to add the ability damage then put a wait and remove it?? W.E was not open it was a rough drawout.
You can't level up Claws of Attack +<whatever>.