The 'Team' game mode is one that requires teamwork. You can choose your team by skins. Special skins don't count.
This will only work when you have a lot of team mates. Basically swarms are large groups formed by one team, many slugs varying in size. A swarm has plenty of advantages, like when one slug dies the others can easily scoop up thier mass, preventing the other teams from stealing it. Swarms are nearly impossible to destroy by yourself.
The behemoth slug of one team is vulnerable, and since these slugs usually hold most of the mass the makes your team win, when they fall so does your team. So sometimes smaller slugs hang around their behemoth slug, killing enemies and ready to swoop in if the behemoth falls. It's like a much much smaller version of the swarm.
Like the assistants, sometimes smaller slugs hang around a much bigger one. However, these slugs go inside of the behemoth slug, perfectly camoflaged and if the behemoth falls, the mass instantly goes into them.