Protips: 1. Maximize Item Spawn Rate and Rarity. Loot sells for much more than all the gold you get for a whole level. 2. Gear stats are more important than raw dmg. Get +25% Cash and +25% XP on everything. 3. Only buy/craft Lasers. All other weapons suck. 4. Only craft x2. And only craft if you can't beat a level easily.
Batgang is actually very useful. The trick is to aim the Kicker as low as possible, NOT at the "optimal" angle. This shoots you with super speed horizontally, which makes you hit more bats and keeps you in the middle of the screen, which makes you hit more batgangs, which increases your speed, which makes you hit more bats, etc. Use Smash to bounce up when you eventually lose altitude. TONS of gold per run. Don't have to dash or anything.
Thunder Dragon is the best. Just spam Shock for ranged damage 10, either while flying or just sitting in front of enemies. You got the health, who cares about getting hit?
To win the last race, use a fully upgraded Muscle Man. Somehow, it levels the playing field with the AI, probably because you aren't using the best car so it decides not to cheat and gives you a fighting chance.
 "Realm Grinder"){kind=icon}
 "Battle for Blood"){kind=icon}
 "Sky Quest"){kind=icon}
 "Kick The Critter"){kind=icon}
 "Great Dungeon in the Sky"){kind=icon}
 "Offroaders 2"){kind=icon}