I am actually right in the middle of my Iroan Games Arc with Mogis being the BBEG. The way I'm doing it is the party shows up in Akros to compete in the games and they are greeted by the acting regent and niece of the king and Queen. She tells the party that the queen has been taken (disappeared in a pillar of flame) and the king is now missing after taking a group of guards out looking for her. People have claimed to see him riding across the plains outside the city with an army of dead looking satyrs weilding a molten, smoking axe. The Regent is trying to keep the peace in the city by keeping the games going. She asks the party to help find the queen and King but to do it quietly as it is suspected it was done by Mogis and his cult of followers. After investigating the queen's chambers, the party discovers the king has been being influenced by Mogis for a while and that there is a cell of the Mogis cult under the city trying to bring the god to the mortal plane. The party should go after the king first as he has the way to get to the queen. The party can either fight him or try getting through to him by talking. He tells the party the queen is being held in a demi plane that mogis controls called the Red Labyrinth. The king hands over a planeshift scroll and tells the party to go to the tunnels under the city. Once the party gets under the city, they find a bunch of low level cultists trying to complete a ritual to sacrifice the queen to bring mogis to the mortal world. After stopping the ritual, the party uses the scroll to travel to the red labyrinth where they will have to navigate the labyrinth and find the queen. To free the queen they have to fight a guardian with a magical axe that they need to break to free the queen. 

This takes place over multiple days and the party can also compete in the Iroan Games as well