Playing for the first time? Good for you! Found four Venus Djinni yet? Great! Go unset them all and summon Judgement.
Felix standing up to Saturos and Menardi at the top of the Venus Lighthouse to convince them to let him take Sheba back to the ship, despite being very out matched and standing no chance against them.
Followed by Isaac and the party beating Saturos and Menardi and then after they fuse into the Fusion Dragon, beating them again.
At the end of Golden Sun, due to an earthquake, Sheba falls off of the Venus Lighthouse, most people would let out a Big "NO!" and sob as they failed to save someone. Felix jumps off right after her to save her and succeeds without any injuries.
Golden Sun: The Lost Age
Beating Poseidon, something no one had ever done before.
Piers being Genre Savvy enough to know that after Felix lights the Jupiter Lighthouse, Karst and Agatio will likely try something. He's proven right as Karst and Agatio try to kill them and the party can easily hold their own as Jenna and Sheba show up to help and Karst and Agatio get annoyed because their plan is backfiring. This can end with the party defeating both Karst and Agatio.
Traversing the Mars Lighthouse. Blasting ice with fire was never so satisfying. Saving the world while doing so? Priceless.
The sheer determination of the party to light Mars Lighthouse, despite the Wise One's interference.