Map Making Help Centre

[ZeusLT]

How do I gain a custom hero skill via trigger ?
For example:
I make fake item, added it to shop

critical strike
----Events
------Unit - A unit Sells an item (from shop)
----Conditions
------(Item-type of (Sold Item)) Equal to Critical Strike
----Actions
------Unit - Add Critical Strike to (Buying unit)
------Item - Remove (Sold Item)
But it doesn't work

Then i read some topics about custom spells.
They said that custom doesn't work but default works.
Then I have made Trigger like this but with default spell but skill level up doesn't work..

Is there any way to make custom skill.
or Default skill with lvl up thing?