Go to Altissia and take the gondola that travels down the singular light blue line, then follow the other singular line (purple gondola) to reach the Totomostro monster battle arena that allows you to place wagers on monsters as they fight to the death. When you are victorious, you are awarded medals that you can spend on various rewards. One of the rewards is a Great Garula Tusk. This item costs 2,500 medals and sells for 700 Gil to a vendor just outside the arena. This may not be the quickest method to getting Gil, but the majority of it can be done while you are doing something else, like watching TV. Other options to earn Gil, such as Hunts, require nearly as much time and take a lot more attention. Simply place the wagers, then do something else while you wait. You can get over 1 million medals in approximately 80 minutes. Thus, you can purchase 400 Great Garula Tusks and make 280,000 Gil. This is limitless, as you have to buy all of the tusks and then sell the 99 when it gets full to buy more, which can become a bit tedious. However, this is one of the easiest ways to get Gil in the game. A good method when placing a wager in the battle arena is to inspect the odds of each combatant and then check their levels, condition, and the amount of units they have in combat. Typically the combatant with the most units tends to win a battle, unless there is a large level difference. For the fights with multiple teams, normally choose a safe bet and place a small wager. Stick with small bets for the first 10-15 fights to get a good feel for it. You will soon figure out who are the stronger monsters to bet on. The big wins come from the 1v1 fights, as these are a lot easier to predict. Using the same formula as before, choose the one with the better conditioning and higher level, unless it is a 3-4+ vs 1.