If by Gush, I'm assuming you're referring to the Gush Towers from Elemental Tower D.
A rough idea of how the trigger is set up would be something like this.
Code:Gush Events Unit - A unit Is attacked Conditions (((Attacked unit) is alive) Equal to True) and ((((Attacked unit) belongs to an enemy of (Owner of (Attacking unit))) Equal to True) and ((Level of Acid Bomb for (Attacking unit)) Greater than or equal to 1)) (Random integer number between 1 and 100) Less than or equal to 20 Actions Unit - Add Crow Form to (Attacked unit) Unit - Cause (Attacking unit) to damage (Attacked unit), dealing 150.00 damage of attack type Spells and damage type Normal Animation - Change (Attacked unit) flying height to 200.00 at 100.00 Animation - Change (Attacked unit) flying height to 0.00 at 100.00 Unit - Remove Crow Form from (Attacked unit)
Shouldnt u order the unit to cast Crow Form??