Gyms confuse me. Came across a red team gym with three pokemon. It was a Golbat, a Flareon and something else, I forget which. When I took the fight option, I was given the chance to use a team of 6 of my pokemon, yet I've only ever been able to choose one in the past. What governs this?
Also, once I took it down, and assigned one of my own, I was able to fight my own pokemon to (slowly) up the prestige level. Interesting that this is allowed. Regardless, there was no one else on the yellow team nearby and my Hypno was only 877CP so it was back to red team before I got home 10 mins later...
You get 1 Pokemon to train at a gym held by your own team and you get 6 to attack a gym held by an enemy team