On round one, you can type /ability shaman, take health, then increase health, then use /ability shaman again, then wait after cooldown, and repeat.
Shaman can be used a major exploit simply because of one change :
On the start of shaman, it requires 10 health to increase health. So with 2 players, with a single farm, you can increase your health.
Basically, every round it allows you to increase health ONCE. However, if you reuse the command (/ability shaman), then it resets and allows you to use it once more, while keep your health. This allows people to get max 6000 just at the start of the game.