Hey fellow Final Fantasy X fans! When it comes to side quests in the game, there are a few that you definitely shouldn’t miss.

1. **Monster Arena**: By capturing fiends throughout Spira, you can unlock tougher enemies to battle in the Monster Arena. This is a great way to level up your characters and earn some awesome rewards.

2. **Celestial Weapons**: Each character has a unique Celestial Weapon that is incredibly powerful when fully upgraded. Be prepared for some challenging mini-games and tough battles to unlock their full potential.

3. **Dark Aeons and Penance**: After defeating Sin, powerful optional bosses called Dark Aeons will appear in Spira. Defeating them and the super boss Penance will test your party to its limits.

4. **Blitzball**: While not technically a side quest, Blitzball is a fun mini-game that you can spend hours on. Recruit players, level them up, and dominate the league for some cool prizes.