How about dead bodies? There might be casualties of the zombie attack...
And how about this (http://www.thehelper.net/forums/showthread.php?t=67207) dangling down from a telegraph pole?
Lol got so many goblin quotes you didn't use any of mine?
Brutillus the Malebranche (I'm assuming he's a sadist): Argh... Fresh Meat!!! (You could play the sound) :)
No. 1: It leaks...
For upgrades, create custom upgrades from your Object Editor, then do Set Level of Upgrade to (whatever). I cannot use WE now, maybe later. Sorry.
Perhaps telling us the theme... like ice or fire or chaos or something.
Lightning Burst - Fires a bolt of lightning in a target direction. Units that hit it will be shocked, taking damage and being knocked back. Channeling.
SFX: Continuous chain lightning effect from caster to target. Shocked...
Make ground pathing blockers to stop normal creeps from running amok, but make bosses and builders flying. (With 1 height or something... :D)
Hope this helped.