In Arena when you choose battle mode "Deathmatch" and "Team Deathmatch" you can set a bet. Its maximum value depends on the current level of the General, which you want to fight in this battle.
Winner gets everything!
In the battle mode "Deathmatch" - winner is the only one remaining alive, and receives the prize pool (players' bets). In the battle mode "Team Deathmatch" - the surviving players of the winning team - share the prize equally.
Hint: You don’t need minibots or credits to take part in training combat. When you win, all resources collected on this setting, during combat with Aliens, will be added on as a prize.