How about, not using any trigger, hm?
Okey its very simple now:
1. Open your map
2. Open Object Editor
3. Click on "Abilities" tab
4. Selected ability which the Goblin will cast
5. Click on "Art - Animation Names" and change it to the animation which you want the Goblin to play.
If you don't want it to play any animation, delete all strings from the list in the "Animation Names"
Simple, isn't it ?