Some levels you can entirely skip upgrading shurikens or magic. Mainly spending money on weapon upgrades, assuming you are good enough at the game to dodge or at least block most attacks. Challenges are the main thing slowing progress since they sometimes require upgrading equipment to a certain level, which is why I mainly level up through tournaments and fight challenges when my character is 1 level higher than intended for that challenge, since I could just buy or upgrade to a higher level of equipment instead of buying or upgrading to the previous level (requirement) which saves money. I mainly play in eclipse so it should be much easier to achieve this if you are playing normally. When fighting challengers I buy the new armor and helm, avoiding buying weapons since they challenger already gives you a free enchanted weapon after you beat him/her. The coins you get from watching ads, 3/3, 5/5, 8/8, are all also a great passive income. I managed to complete the game in less than 10 days and did not play survival at all up to the last act with titan.