I only played this originally when it first game out back in November of 2016 before all of expansion pass content. I did take advantage of some of the content that slowly rolled out at the time such as some of the time limited event such as the Moogle Chocobo Carnival. Although there is no telling if this event is likely to return for FFXV Windows Edition owners.
Anyways one of the most notable things I learned was Rare Coins and Debased Coins are extremely important for fast leveling and are to be never sold for money. 8 Rare and 24 Debased of these can be used to become Expericast Spells which give a fixed amount of exp when casted against enemies. 12 debased silver pieces, or 16 debased banknotes also work.
Rare Coins can be farmed in the Cleigne region. Find a shining blue farming location and simply save your game. If it's not a Rare Coin when you pick it up, reload the save and try again. 8 rare coins gives 96 exp rank and +2 casts, but 24 debased coins gives 96 exp boost but +6 casts, so if using debased coins, use in the highest multiple of four up to 24 you can.
Don't use more than what it takes to get to 96 exp rank. The difference between 96 and 99 is small. Using a 9th Rare coin for an additional 3% is wasteful because the coins give 12% each. Better to save the 6th.
Expericast spells give you a flat experience bonus when immediately casted on enemies. Strength of the spell has no bearing, so using a strong Firaga spell will not give you more experience than a weak Fire Spell, so basically use 1 Fire element and the required amount of coins to get a bunch of weak fire spells. Also using these against a strong enemy won't give you more exp, So using these against weak enemies is quicker and has the same result.
Earliest time to do this is Chapter 3. Create your Exp Cast spells. Visit Wiz's Chocobo Ranch and eat the Triple Decker Sandwich for 50% EXP Boost. Go find weak enemies like Sabretusks around Hammerhead with EXP Boost active. spam your EXP spells on weak enemies as fast as you can.
Expericast gives about 140 EXP per level so at Lv. 96 that's 13,440 EXP. with 50% Food that becomes 20,160 EXP and using the Inn at Galdin Quay is 100% which means 40,320 EXP per cast.
You get 5 Casts using 8 Rare Coins (3 +2 Bonus). So that is just over 200,000 experience points.
Later on in chapter 9 once you reach Altissia can go Maagho's Bar and eat 100% EXP Boost Lasagna and the Altissia Suite is 300% EXP which doing the same gives you just over 400,000 EXP.
I think doing it earlier in game at Chapter 3 with 16 Rare Coins to get roughly the same amount of exp for the time you get to Chapter 9 might be worthwhile.
200000 EXP is enough to raise your ENTIRE party from level 1 to 41.
I originally did this super late in the game, but even so the results speak for themselves -
https://www.youtube.com/watch?v=FfMVzzo5_ic
If you don't care about game balance and want to power level through everything, use this if you like. If you want to take your time with the game, ignore this.
