Most of the things that you can purchase are cosmetic, such as the katana and cloak upgrades, but the scrolls are the one thing that are the most useful. For attack scrolls try to save them for when you reach the boss, as the bosses can be very tough to beat and the scrolls are a great way to get an extra advantage.
Defeat Bosses
Beating the bosses can be tough at first, but after you get the pattern down, it's easy. Don't let yourself get hit by the green projectiles. Avoid them, then when the boss head flies at you, avoid that, or slash it really quickly. When the giant mask head floats in front of you slash it over and over until it moves again. Repeat until the boss is killed.
Earn More Coins
If you want to earn more coins, the fastest way to do so is to stick close to the ground hitting as many jars as possible, or hit the jars that are suspended from parachutes. If you see a pink jar, hit that and you will get the golden cat. You'll earn one random prize at the end of the level if you get the golden cat, and oftentimes that prize will be coins.
Jump
Do not forget your extra jump. It can be activated at any point between attacks.
Jump Strategy
You can jump by tapping the left side of the screen or slash by tapping the right side of the screen. The height of your jump depends on how long you hold down on the screen for. No matter how high you jump, you can also double jump. For the second jump, the same rule applies for how long you tap the screen for.
Saving lives
Do boy try and hit everything, if things are getting tight. Saving your lives and getting through to the next level is paramount.
Slash and Jump
When you slash and hit an enemy in midair, you will rise slightly, but not a whole lot, so you will have to slash fast in order to hit a mask that's at the same level as the one you just hit. If it's slightly below, slash quickly at it, and if it's far below, try to slash it or jump over it, depending on if you think you will fall right on it or not.
Attack Scrolls...