If you are reading this, you haven't got a clue on how to complete Return of Harmony Party Quest (RoHPQ).
First, go to Canterlot via the Ellinia boat. When you get there, move to the left, enter the castle, keep going left, and talk to the Princess Celestia NPC with a party of six. You won't play as yourself, and each player will be assigned to one of these ponies: Rainbow Dash, Pinkie Pie, Rarity, Applejack, Fluttershy, and the leader of the party, Twilight Sparkle. After a cutscene, you will find yourself in a hedge maze. Simply navigate the portals while fighting Discord's monsters (apple puppets, evil balloons, evil butterflies). The maze will abruptly end with the person playing Rainbow Dash hits a certain point in the maze and acquires the Pegasus Wings. Another cutscene occurs, and the Rainbow Dash player goes off to play a minigame.
Now, you're heading to Twilight Sparkle's library. The goal is to make it while the other players receive their own points if they block your attempts. Once you reach Twilight Sparkle's library, a miniboss battle against Discord appears. You cannot win without the Rainbow Dash player, so don't bother trying. A cutscene happens, and every player but the Twilight Sparkle player has to play a minigame. The Twilight Sparkle player than has to navigate a map and find each player except the Rainbow Dash player. When all the other players are found, proceed to Suspicious Cloudsdale 1 and play a lasso minigame to catch the Rainbow Dash player.
Once all players are together, you must equip the Elements of Harmony equips that are in your inventory now, and find Discord. Now you can finally fight him. He has 100,000 HP. He moves around the screen, throws explosive chocolate milk projectiles and repeatedly spawns ballerina buffalo mobs. Once his HP is under 10,000, every player must use the Harmony Blast skill (under the beginner tab in the skill menu) at the same time. A cutscene will occur, and you will get your reward (500,000 EXP and a Discord Statue) and be transported out of the PQ. Collect 10 Discord Statues and you can receive a Element of Harmony that you can take outside of the PQ, with stats that go up by 1 for every EoHPQ you run.
Edited by Toxie, 31 March 2012 - 06:43 PM.