Hey there, thanks for the demo!
Some constructive criticism and critiques:
-Player initially spawns behind the training dummy for some reason
-Certain enemy projectile's such as those of the scorpion are on the wrong layer, so blood splatters obscure them and make it very hard to see the projectiles once the screen fills up.
-Astro's main attack "Knockback" is backwards for the X axis. Shooting the dummy at the start while on the left of it makes it move closer to you rather than getting knocked back farther.
-Astro's main attack doesn't get any damage increase for several level ups. This is the issue with starting with really low numbers. In order to move from 2 damage to 3 damage, a single point winds up being a whopping 50% damage increase. If you simply increase all the starting values so the weapon is doing 10 damage a shot (And of course increase enemy HP along with that), then you can easily do a single point per level, so getting 10% more DPS per level which isn't bad.
-Please change the AI of the enemy birds so that they're not constantly hovering in walls where it is impossible to shoot them
-For the engineer's Mine ability, please reset the count to full once the player goes down to the planet. Currently if I drain my mines on the ship and have say a count of 1, I enter the planet with the count of 1. This means I have to now sit there and wait for the count to refill at a slow pace.
-For the engineer's Turret, there doesn't appear to be any way to upgrade it, despite the prompt.
-Either the player's hitbox is too big, or the projectile hit box is too big. I'm taking damage from projectiles which based on the sprites clearly didn't hit me. A good rule of thumb is to make the player's hitbox slightly smaller than the player, and make enemy hitboxes the full size of the enemy. This helps ensure that the player isn't taking any cheap damage that should've been a "Miss"
-A minimap would be SOOOO helpful when trying to locate which of the dozen "rooms" the enemy is in.
-Dodge abilities should be set to where the player is moving, not where the mouse is looking. The mouse is typically looking towards an enemy, and if I'm dodging, it's probably because an enemy projectile is coming right at me, thus in the vast majority of situations, rolling towards the enemy is the exact opposite of what I want to do.
-The "You are Dead" screen doesn't display any of the information, also is says "Time Survied"
-Game should auto pause when not the active window
-Keep running into this one weird object on every level, it's a few vertical lines but for the life of me I can't figure out what it is supposed to be.
-The large Golem type enemies frequently turn invisible when they take damage. This is very confusing because I can't tell if they're supposed to be dying, if they're glitching, experiencing iFrames, or what is supposed to be going on when this happens. If you're doing iFrames, then I suggest a flash or adjusting their image_alpha rather than making them completely invisible.
-Consider having a "Press Enter to move to next level" instead of having the player spend two minutes backtracking trying to find the randomly spawning exit.
-Boss attacks do WAY too much. I actually saw my HP drop to -84, so a single attack is doing over 90 damage?!? So I have to hit him over 100 times, and he gets to kill me in 1 or 2 attacks, and he gets to have over a dozen projectiles flying around at once?
-Please make it clear what the pickups do. Saved 100 coins for a chest, and have no clue what it did. Also if the pickups would activate immediately upon open the chests it would be nice, instead of having to wait there for a second for no reason.
-The Meno character actually isn't as unplayable as it first appears. I was able to clear the level with it, mostly a strategy of timing the Roll (To close the distance and take advantage of the iFrames) and activating the Lightning Hammer in the middle of it. You'd need some seriously good loot drops to be able to kill the boss with him though.
-Finally managed to clear the boss with the Engineer. Engineer is incredibly overpowered. Just turtle up during the level with turrets and mines, and send out your drones to do your dirty work. Prior to the boss battle I laid 50 mines all on top of each other, which the boss took like a champ, did only about 30% HP to him with that. So I'd imagine laying 175 mines prior to the boss would allow me to instant kill it.
One thing I would really suggest is looking at the design philosophy of Castlevania. Unless a designer is able to beat the boss without taking ANY damage, it isn't put in. Again look at Enter the Guneon, every boss can be beat without taking damage, there are even in game buffs and achievements for doing so. I honestly don't think anybody would be able to beat the boss using Meno without taking damage. Meno would really need a "Recovery HP while attacking" item.
Even though there is a clear tier system Memos<Astros<Engineer, still props for making three distinct character classes with their own style. A LOT of developers use carbon copies or characters with only slight variations, but your characters are three entirely different entities.
Despite my frustration with the boss battle, it's a good boss. Starts off with the creepy atmosphere and lighting to set the mood, it's huge so it feels intimidating, things get chaotic very fast. Certainly better than most games boss battles which simply follow the formula of Bullet Sponge + Infinite Adds. Since the boss is so big, you may even consider including weak spots on him for bonus damage.
I can really see some players trying to master the Menos as it clearly has the highest skill ceiling. It was also nice to be able to play a shooter and not have to worry about ammo. In other games, I would NEVER fire off my power weapons like homing drones, because what if I needed them for later? With the cooldown system, players get to have their cake and eat it too. I'm able to enjoy using my big guns without worrying that I won't have them available when a boss or big enemy comes. Speaking of big enemy, I enjoyed the randomly generated larger normal enemies. All in all I enjoyed it. I found it tough but fair (With the exception of the hitbox issue, easy fix though).