Finally finished putting together this patch.

Achievements have been added to the game now, and are compatible with GameJolt/sync up with GameJolt. Also, “Mirror Mode” was added, which unlocks when you get 5 achievements.

Full details of this release below:

Ver 1.0.0.8 (October 4th, 2014)
+Added unlockable “mirror-mode”
+Changed background drawing function to no longer use AlphaComposite if it isn’t transitioning between backgrounds, which should improve performance
+Fixed a minor bug in the options menu where pressing escape there caused some odd behavior
+Fixed a missing flag on one of the exp capsules
+Made the “pick language” dialogue box a little less ugly
+Fixed a minor issue with the key set menu where the OK/jump button wouldn’t work unless it was pressed twice (it was ignoring the first keystroke due to not clearing the key buffers)
+Nerfed the exp table a bit to make the “Max HP” achievement more attainable
+Firing of the gamma bubbles in the boss’ “rage” mode made slightly easier to dodge
+Tess now has boosted friction for a frame when she lands from a jump, which should prevent some slidey-ness that used to occur with precision jumping
+Tess no longer does the “twitchy-moon-walk” when you hold both the left and right arrow keys
+Tess no longer jumps to the left if you jump while holding both the left and right arrow keys
+Tess now has (very negligible) air resistance, but you probably won’t notice it
+Interact key now works as OK in options menu
+Added ”よぉぉぉぉ” back to Japanese translation