Considering that when you beat the game, you will only get around 15-25 crowns if you do every single one, the best strategy is to do the same one over and over until you reach 100. I found that the one in thrills of the nether deep quest is the easiest as it gives you one right away and all you have to do is complete it then return to the hub, then go back. Rinse and repeat this method. Hope this helps.
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