Some more info about the gametypes:
In Mongoose Doubles, each team has got two mongooses per base. Mongoose Doubles is intended for 8 squads of 2 players. The spawn for the vehicles is set at 1 sec, so you'll always find a spare quad. There are 24 mongoose on the map (the gametype actually changes all of the vehicles into mongooses). When you die you'll spawn in a safe area, here you can pick your vehicle or wait for your bro to repawn.
Mongoose Slayer is intended for 2 squads of 8 players. It is a variant of Bro Slayer, so you repawn is made easier.
In both gametypes your speed and jump height is decreased so to prevent camping. You spawn with rockets and fuel rod guns with infinite ammo.