Changes

When training you’ll have to choose 1 pokemon. So choose wisely. You don’t have 5 backup pokemon to help you out.

Every time you beat the pokemon that’s already on the friendly gym, the gym get’s prestige. How much depends on a number of factors, but it seems you gain more prestige for the gym if you beat it with a pokemon that has a lower CP than the pokemon that’s placed on the gym. The more pokemon you beat, the more prestige you gain for your gym. So even if you can only beat one pokemon and lose to the next pokemon on the gym, you still gain prestige for the gym.

When that pokemon is knocked off the gym it will return with 1HP. So you don’t lose your pokemon, you lend them to the gym.

Fun fact: if your pokemon is the one that made the attacker lose it will say ‘Battles won: X’ beneath him in the gym overview screen.