Witches study various ancient mysteries, but some mysteries are too arcane even for them. Such as retro technology.
This game is largely based on Falcom's 1984 Dragon Slayer, with my reference version being the MSX port. Much of the premise is the same: you collect different power-up items and bring them back to your base, which allows you to level up to allow you to fight stronger monsters and in the end you face the final boss -- which is the Dragon in Dragon Slayer, and the save icon in this game.
The initial enemies can easily kill the player, and the first course of action would be to start collecting various colored coins and bring them back to the purple magic circle. You will learn new magic spells as you kill enemies, and once you have killed 99 enemies (there's a counter on top-right) you can take care of the save icon and finish the game. Each time you kill an enemy, the game will spawn a new one, and they'll be stronger than before.
The rough estimate to defeat the boss is +5000 ATK and DEF, or there might be an easier way.
Falcom claims Dragon Slayer to be the first Japanese Action RPG (Hydlide also disputes this claim) and as such it is well-respected, but I found it to be not quite well-playing. In Dragon Slayer, the player can collect multiple power-up items and bring all of them to the base at once, except the crucial one that increases Attack which must be carried one at a time, around ~160 round trips.
Also, after the player slays the Dragon in Dragon Slayer, the player needs to find three "Crown" items that scatter to the random places, all the while fending off unbeatable ghost monster who will randomly take away your items and drop them in random places. I completely cut this part, as I found it an exercise of frustration. With these two major changes, the game came to feel a bit bland but I prefer a bland game than one that overstays its welcome.
The basis of this code is forked from about 1/4 of the way of Porklike tutorial, and the player character bumping into the wall would feel familiar to anyone who's played it. One of my goals with PICO-8 was to create something like Hydlide, and I think I'm coming close to it.