*Warning* Game Breaking Glitch. Use at your own risk. First click on an item in your inventory. Then take the item to the yellow "OPTIONS" box and click on the options box. While you still have the item, take it to the middle of the options screen and click. The item will vanish. Now you have all the stats of the item added to your character permanently. You can repeat this glitch over and over again until your stats keep adding up.
Adding on to what MiquelLima said. You don't actually have to increase the mana pool to 9999 manually. You can hold down the R key and click outside the game so it will automatically increase your mana pool
The best strategy is to use ONLY THE PISTOL and keep upgrading it (don't buy anything else). Then all you need to do is put all your points into RAMBO for MAXIMUM OWNAGE!
I'm just joking. Follow Trilobyte's wise words instead.
 "Sonny"){kind=icon}
 "Raze 2"){kind=icon}
 "RPG Shooter: Starwish"){kind=icon}
 "Castaway 2"){kind=icon}
 "Dragon Age Legends: Remix 01"){kind=icon}
 "Hands of War 2"){kind=icon}
 "Bullet Heaven"){kind=icon}
 "Not Your War"){kind=icon}
 "Epic war"){kind=icon}
 "The Legend of the Golden Robot"){kind=icon}
 "Neil the Nail"){kind=icon}
 "Burrito Bison"){kind=icon}
 "Ninja Hamsters vs Robots"){kind=icon}
 "Bloons Tower Defense 4"){kind=icon}
 "King's Guard"){kind=icon}
 "Zombie Splatter"){kind=icon}
 "Bubble Tanks 3"){kind=icon}