The Pit is a round-based game. If you're team 1, you must fight 25 rounds of enemies without losing your coureur de bois. Every round you get a certain amount of wood, which is used to buy units. On rounds 3 and 15 you get a tower; use them wisely. Note that walls are unkillable.
There is a little cheat where if you kill a hidden unit named "AIGuy" you get artillery foundries.
Player 4 (team 2)'s job is to simply kill team 1. You have 25 rounds to kill team 1. Note that surgeons, stables, barracks, and artillery foundries are unkillable (but outposts are, and you may want to get them down to endanger your opponent's villagers.)
This is a very fun scenario, especially if you like small skirmishes.