There's one key method to getting more heroes in DOTA Underworlds - basically, you need to level up on every level (try saying that when you've had a skinfull) in order to increase your Unit Heroes and get rare, powerful units from the shop.
The trick is this: in order to level up within a level, you need to have a certain amount of XP - the more XP you have, the more levelling up you can do and in turn, the more heroes you can get.
You'll basically need more XP than your opponent in order to level up, so before you join a fight, make sure you're checking the level of your opponent by going to the player-list on the left-hand side and looking next to the player's name.
Starting a battle in each round awards you 1XP, and you can also use gold to buy more XP, if you want to. I wouldn't recommend spending all of your gold on XP, you really will need it for other things, but it's a nice quick shortcut if you need it. You do get more gold at the end of rounds and by performing streaks, though, as well as winning a battle.
Fighting as many battles as you can with lower-XP opponents to collect XP and Gold is the key, then, to quickly levelling up and getting more heroes.
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