Pretty cool remix! All the aside from the out-of-tune xylophone, here are my thoughts. The main melody synth you replaced sounds a little too whiny, maybe try adding a low pass filter?
The drum buildup is great, good job with that. The drums at the drop feel slightly out of place, but the variation between only kicks and kicks + snare is good. Windows error sound is a nice touch, but it’s still out of key, you could have transposed it a little, but again it’s a nice effect. At 2:30 (calm part) the drums could be changed or at least in volume because they feel like they should be used for dubstep, or only at the drop. The end is also pretty nice, my only advice there would be to add some reverb to it.
Anyway, great remix!
Edit: it’s out of tune because it’s higher than it should be by around one semitone.