Thanks for the fix, yeah, it'd be a good idea to use the default items as reference for sizing.
I was wondering about that spider, wasn't sure if hanging enemies were even possible in the engine. About the gas, you could make them spit that gassy green projectile like the engine's plant enemies can. Remember that we're not making an exact remake of the game, so feel free to change what you need to to fit the engine's limitations.
There were actually a couple of objects I did need for when you get the time, which are the warp and shop stones. You could probably use the save stone you made as a base, the writing is the same, all that really needs to be changed is the top image and gem.
I took a couple of ingame screenshots for reference: