I think this might be a good time to explain how the level and upgrade systems work, since it helps understand the game a lot better.
There are 150 levels, and completing each one unlocks the next. You need sunstones to purchase permanent upgrades for your character. I switched the currency system up a bit by making it persistent, meaning each sunstone has a set location in the game world, and once you get a particular sunstone, that sunstone is now gone forever when you replay that level. During each level, and when you look at the level list, you will see the percentage of sunstones you have found already for each level.
This adds a bit of treasure hunt, and also helps balance. Hardcore action players will plow through without looking back, while others may want to make sure they have gotten every last sunstone and upgrade. You should know that like a Metroidvania, you will need certain upgrades in order to access certain areas, like bombs to open passages, or wall jump to scale cliffs.
Anyways, here is a quick snippet of the Hydra. It a really tough enemy that shoots fire balls from each of its heads, and if you get up in his face, he may try to swing you around a bit. You definitely don't want that.