Oookay.... I got one shell stuck in a loop, it's just bouncing up and down on one launcher (with no turrets in range) so i'm going to leave it here and eat lunch.
A fix for tactics: there is no reason to help EN1 help kill EN2 other than it will help rid EN2. What you should do is stockpile troops and either 1. Attack EN1 or 2. Attack EN after he kills EN2. The solution to this would to be each time you take down an opponent, a "secondary" spawner is created. This is slightly weaker than the original spawner, but provides a edge against players who hide in the corner instead of fighting. Just an idea.
@Dhalaegho dont ask me how i know, but enchanted items are NOT more likely as a drop from any given enemy when your level is high, but because you will fight more and stronger enemies, your overall chance that one of them will have one is high, not the drop rate.
Glitch update: You don't have to hold enter. You can just hit it slowly as many times as you want, and this was, your money doesn't go negative!=======
(Original glitch: Select a tower. Hit Tab until the one of the upgrades (NOT THE PICTURE) is bordered with yellow. Press and hold enter. Your money goes negative.)