The enemies in Bloodstained: Ritual of the Night can be punishing if they hit you so make sure you avoid them whenever possible as you never know where the next health-restoring save point might be. The best strategy to defeat them without sustaining damage yourself, especially during boss fights since they are capable of dealing huge amounts of damage in a short period of time which even healing potions will not full replenish is to spend time studying their patterns to see if they have a weakness you can take advantage of.