Getting all the gems took a bit and required some creative thinking, but I can verify that they are all possible to get in single player mode. Some things to think about if you get stuck on one:
1. Ladders can be moved by the environment, and it's not always bad if they are. after a ladder is placed, the height of it does not change.
2. Ladders are not effected by spikes. They can stand safely on spikes, while you cannot. Use to your advantage.
Something to add might be a better filter in what drops you keep. For me, a ranger, I'm not interested in all the swords/staffs/axes that drop, nor the offhand tomes and daggers. Adding a filter for ranged/magic/melee might be nice.
In regards to the wheel sizes, there are definite benefits to using small, large, or combinations of wheels. The small wheels bring the shooter closer to the ground, allowing for more accurate shots, especially with weapons like the gauss rifle, but it's wheel spikes do considerably less due to the size. The large wheels are amazing for rolling over everything, but are better suited for use with weapons such as shotguns of launchers. Needless to say, the large wheel spikes kill mostly everything. The normal wheels serve as a happy medium between the two, with average attacks and pretty good spikes. Depending on your weapon choice, wheel size can make a big difference.
Dear Moshdef,
I believe we are not of the same religion. See, to most people, it's actually Easter Tuesday, not Monday. Sorry for the misunderstanding.
"Trust me mate, the wheels you just had on this car don't fit on this other one."
"But they're the same size. They are the SAME wheel."
"No, they're completely different. Trust me."
The game's overall GUI could be cleaned up considerably, it's a little bit cluttered. This seem to be mashing into each other, and it's kinda nasty. The game itself is excellent and balanced, but if you retouched or overhauled the GUI it would be really nice.
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 "Steampunk Tower"){kind=icon}
 "The Peacekeeper"){kind=icon}
 "Memohuntress"){kind=icon}
 "ClueSweeper"){kind=icon}
 "Battle without End"){kind=icon}
 "Just Trolling"){kind=icon}
 "Nuclear Outrun"){kind=icon}
 "The Ice Temple"){kind=icon}
 "Earn to Die"){kind=icon}
 "Clash of the Dragons"){kind=icon}
 "Epsilon"){kind=icon}
Are you a Scientologist?