Area 4 frame made up. I pretty much make the frame out of black tiles and test it all out.  There are a few things I look for while testing at this point. Make sure all the jumps can be made. Check for any awkward movement through narrow corridors. See where the camera goes in some of the bigger rooms, and ensure the player can see what I want them to notice (ledges, visual clues.) I'll also load in some of the ability barriers at this point. I like to get a good sense of where certain obstacles are going to be in a room so I can plan what the background image should look like for that room. In earlier areas, I waited until after some of the art was done and re-tiling to accommodate the size and functionality of certain barriers added some time.

Area 3 enemies are mostly done. Just some tuning/balancing left to do. I mostly have them placed where I want in the level. I try to have a reasonable mix of enemies that are just bullet sponges and enemies that are puzzles that ask for a little more attention from the player to take down. On that spectrum, I tend to lean toward bullet sponges, especially since this is a metroidvania game where backtracking is encouraged. It seems like that backtracking will be more appealing if the player doesn't have to keep stopping to square dance with each enemy over and over as they try to progress. I more prefer to build the sense of empowerment by basically giving the player more powerful bullets, that blow up the sponges much faster than the early weapons in the game.