Advice for beginners: Don't bother buying any stock above 30, or sell below 70. My benchmarks are buy at 25 (or below), sell at 75 (or above). I've seen in the 10s and 90s, but they're really, really rare.
For the Lone Wolf achievement: You have to kill Bill WITHOUT giving him pain pills, repair the fence and hook the generator up to it, brick up the window, and find 4 bullets. It requires some clever movement around the map, and I was left with only 20 minutes on the clock at the end. Killed the very last zombie with my axe
Am I the only one concerned with Gary's obsession with the pizza girl? Since he is clearly ordering insane amounts of pizza, enough that he can casually give you 80 pieces at a time without a second thought. The pizza place must run purely off of deliveries to him.
Love this game. Make sure you keep the damage of each hero balanced due to the nature of the damage types, and go for the abilities in the level-up screen. They're free to use and can be very powerful
Very good game, excellent level of difficulty. Some comments: Mage towers are more expensive than archer towers, but are otherwise almost exclusively better once your hero can solo golems, due to their ability to kill ghosts. Your hero can basically solo golems after you level his health and damage a few times, so by level 2, archer towers become rather useless. Something to keep in mind for current players and any future sequels
Spy is the best unit ever for rescue missions. Just sneak into a base, rescue all the civilians and the VIP, perhaps level the building as you leave, then evacuate and let the rest of the units mop up the baddies
Challenging game, don't upgrade Vulcan. I use it so infrequently it doesn't help. And saving up for the 1000 point gun is TOTALLY worth it. It gets sooo much better.