@kalel01260 I made sure to have the white tiger and lots of high damage units. Save your mana until you get to Inferno (or have 100 when you get to him anyway) and then just spam the dmg increase spell from the white tiger. I got him when he was about half way back to my hero.
For those looking to beat greg. Equip one of your characters with freeze and someone else with poison. Class and which item doesn't matter. Freeze is makes it doable and poison decreases the time it takes to kill him by ALOT.
Overall, this game has a lot of potential. Some suggestions though. 1) Giving the pistol a short range is annoying. 2) Fewer monsters per wave/fewer hits per monster would make for more interesting play. 3) Some kind of tutorial wouldn't hurt anything especially since things like the store come as a surprise and are nice to use the first time.
@asmun I have managed to get to 1013 VERY briefly. Homing actually seems to do more harm than good at the end as it means everything is going for one enemy rather than hitting lots of different enemies like non-homing does.