Tips for losing no lives:
1. Always be on the move. Never stay in one spot else you're sitting duck and your enemies will surely make meat out of you.
2. Never exchange ranged weapons(especially shurikens) for melee ones for it will be of very great use.
3. When killing off the last enemy for the current screen, make it a habit of sucking their skulls for health because when skull-sucking, your wide open for enemy attack but having no other enemy around means having the time of your life slurping blood from skulls worry-free.

For boss fights:
1. Utilize the Blitz move whenever the gauge is full.
2. Never engage the boss head-on! Your at a disadvantage when fighting head-on. Make single attacks and keep out of the way.
3. When a boss is invincible(their outline is glowing blue), keep out of their line of sight by walking up or down. When their invincibility wears off, blitz them right away.

REMEMBER: Always predict your enemies movements for better strategies. These are just tips.