Coin was supposed to be in Alpha 1.4b, but it was later removed. Coins and money system was supposed to be after you beat the Boss and you will receive 20 coins. In random time coin will appear and when you collect it you will get 1 coin. Coin bar was supposed to be under "You Won!" after level 20.
You was supposed to spend coins in shop and you will be available to buy: Heal Potion, Regen-Potion, TNT and Shield.