Love the bell melody and piano rhythm in "Inside Your World". Very warm and "homey" tone. I generally enjoyed the high hat/click percussion, though aside from the few times it cut out I didn't notice any variation in it. But that's just being nit-pickey. Overall I really liked the song.
First impression of "Behold the Nightmare" is great. Wish the guitar melody was a little louder. Great impact when the organ comes in, though might want to watch the volume on the organ, kinda' drowns everything else out (particularly the woodwind at 1:22). Nice bass rhythm. In your description you mention this is intended for a platformer game, but I could see this song working well in a jrpg or arcadey jet fighter game as well.
"Approaching" starts with some neat bell arpeggios, but you may want to consider decrescendoing as the piano comes in so the piano isn't drowned out (especially since the piano is carrying the melody at that point). Very lovely as the bass comes in and I like that "beep boop, boop bop" sound. Very nice key changes around 2:37. Synth stabs towards the end are exciting and hint at a transition to the next song.
"Inside My World"'s acid bass provides some exciting intensity. The high pitched pad that fades in periodically provides some nice dissonance.