Power is important, but level is also important in determining how much health you have. A level 18 with +12 everything would still die from Mardicus's first attack.
Once you're strong enough for gulu difficult, it's pretty easy to get coins. A pretty common drop there is harm lvl 3, which sells for about 800 coins. If people didn't pay money for coins, the servers would cost too much to maintain and close.
Generic, it wouldn't be fun if the fights were just taking turns hitting each other. You should take into account ground thickness, the opponent's hp and strength, and leftover physical each turn and plan your actions accordingly.
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