Stack Skill help

As i said in the thread called help help help 2x.... how can you make it so if oyu have one stack of item_a it gives you 2damage bonus, 2 stack of item_b gives you 4damage bonus and so on? like if you have one weapons that gives you 5 damage, and you pick up another one, and it stacks up by trigger, how can you make it so if there is 2 weapons of that same type is in one stack, you can get 10 damage.

eh?

create every possible item, if a hero pick up a item and he already has a item of that type remove both items from the hero and give him a new.