First of all, I noticed this game is taking notes from Castlevania, using hearts as currency... The only way you can heal is to buy items in shops or find the hidden hot springs. The shops sell health bottles and feathers that save you from falling... I feel like I shouldn't really need much of those, but I find myself spending a lot of time grinding hearts on all the respawning enemies I come across anyway.
It turns out that grinding hearts IS very important in this game. You can get health upgrades by gaining a certain amount of hearts at the end of a level. You can get new weapons and upgrades by completing special training rooms found in certain stages, but those new items can only be used after you reach a certain amount of health... was this all in the instruction book? Otherwise I have no idea how anyone would've been able to figure that out by then.
The first few stages are vertical scrolling stages where you die if you fall below the screen, like in Ice Climbers. It's pretty easy if you just keep moving forward, but if you stop and grind hearts, the enemies can easily overwhelm you. The 4th stage is the first dungeon, it's a non-linear Zelda II style maze dungeon where you just gotta find your way around.