Prepare to go to war. You can tap in and scroll right to see what lineup of Pokemon the gym has defending it. Battles will start with the lowest-CP Pokemon in that Gym, before moving on the next strongest. Like in the original games, Pokemon elemental types should be considered–water beats fire, fire beats grass, grass beats water, etc.
To engage in combat, the player can repeatedly tap the screen to perform basic attacks, which builds up a special meter underneath the health bar. Different types of special moves have different amounts of meter, which can be saved. Each Pokemon has different basic and special attacks. When the meter is full, pressing and holding the screen can unleash a special attack. Swiping left or right can dodge special attacks. This can usually be timed by observing when the screen flashes yellow and the Pokemon rears up, indicating an incoming attack, but we would suggest focusing on belting out as many attacks as possible instead of wasting precious seconds to dodge.
You can also attack a Gym with members of your same team–the defending Pokemon will take damage from all attackers at once. Teaming up with more people will definitely help with getting a Gym’s Prestige Points down faster!
Defeating at least one Pokemon in the gym will lower the amount of prestige points the Gym has, which will eventually lower its level, meaning that less Pokemon will be able to defend it. Once all Pokemon are kicked out, it will be ready to be claimed by the victor’s faction. From there, you can place a Pokemon in there to defend it, and train at it to raise its prestige and Gym level. If a rival faction takes your Gym away, feel free to get right back in there and fight to reclaim it.
Originally Posted by: gamespot.com