I wish the square leads for Last Battle/Megalovania were more prominent - they tend to be drowned out by the accompaniment (at the part where Megalovania is first introduced - I think even bringing it up an octave would have worked better). As it started throwing in the Cave Story and Undertale tracks together, especially around the 2:15 mark, it began sounding really off for my taste. I think it was Balrog's theme that I wasn't sold on this combination of tracks from Cave Story and Undertale actually working together. Your medley, however, does a great job with flow, changing between the different tracks were reasonable, and I especially like how a part of the Last Battle accompaniment here uses one of Megalovania's instruments.
As for the Labyrinth Zone/Jenka one...I like how the spin is put on the Jenka theme - modified enough to sound almost like a "Labyrinth Zone" addition, but still in tact enough to be recognisable as Jenka's theme.
I also feel as though it would be more helpful to link new mashups both in the post announcing the new mashup in addition to the original post, but eh I guess it's not a big deal.