This is actually insanely boring. Ugly pixel art without animations. Just the most basic fighting mechanics where you attack in turns, but without strategy (at first at least), so there's nothing fun about that. As I said, no animations, so you just sit there and wait for their healthbar to go down. Monsters just stand there motionless, lifeless.
Prestige when you reach world 3 because you're not gonna be able to use those new resources without having tier 3 items. I went all the way to world 4 level 18 before prestiging, which is a waste of time.
Before prestiging, increase all your item qualities to the max you can afford and enhance them as much as you can so your next character is much stronger instantly and all items you buy are much stronger, so you can progress much faster.
Unless you can earn more shards over time, this game is unbeatable. Eventually you'll need 105k pet shards to be able to upgrade it to level 9001 (previous limit is 5000). That would take forever to collect! Same with actually leveling it up! It's better to just spend the time spent playing this game earning minimum wage and you'll become a millionaire and can buy whatever PC and games you want.
Because all the save files got lost, I wouldn't considered it cheating if you were to set the coin amount to a high number to be able to buy all upgrades so you can start the rifts much quicker. That also means you wouldn't have to use candies to upgrade the coin multiplier or the start amount. Of course only if you were already far into the game. You're merely restoring what you lost.
It starts to get really grindy from Abaddon. The amount of lower units you need to upgrade a higher unit goes up exponentially. Even with 3 upgrades it still takes half an hour to earn back the amount of spent Haagenti.