I'm desperately trying to work out the optimal way of getting this. I thought I had it and just lost 2 hours 28 minutes of my time before having to abandon a run. I worked out getting coins in puzzle mode is good way to raise coins quickly. Unfortunately, I wasn't aware that the more points you accumulate and the higher the rank is what increases the difficulty in the adventure. I was expecting to return to the adventure with the same level of difficulty reached so far in the adventure with a full upgrade of powerups, and instead ended up returning to an adventure that needed the majority completed with it giving me 11 chains per level and a full range of colours (except for orange and light blue), which meant I would have had to play almost the entire adventure with full difficulty. I'm thinking the next thing to try, when I have the enthusiasm to try again, is to get the Coin Scarab artifact as quick as possible, and try to avoid collecting gems, but get as many coins as possible, and complete everything apart from Hotan, then go over to the store and buy the fireball upgrades to be able to complete the puzzle mode in one go, and then use the puzzle mode to gain all the coins needed to upgrade and buy everything, and then go and finish Hotan.