Complex sentence: Horza is shocked to see Balveda show up in the CAT and he uses his appearance to stun her, and fearing a Special Circumstance plot, impulsively pilots the CAT out of the GSV in a wild trail of destruction.
Split into simpler sentences: Horza is shocked to see Balveda show up in the "CAT" and he uses his appearance to stun her. Fearing a Special Circumstance plot, he impulsively pilots the "CAT" out of the GSV in a wild trail of destruction.