The 0.2.5 build released with this post has working versions of the "buoy", "trucks", and "wheel" stages (three of the four stages that were omitted from past “unstable” builds due to significant issues relating to the stability of their custom physics parameters when ported to Unity 5 and PhysX 3.3 ) and the three prototype stages, "chutes", "elevators", and "towers" that were demonstrated at E3. The 0.2.5 “unstable” build also has experimental implementations of two new character attack moves, head-butts and dropkicks, head butts are triggered by pressing the jump button immediately before holding the duck button, dropkicks are triggered by pressing the jump button immediately before holding the kick button (the specific forces and other parameters for the moves are currently provisional and granular modifications will need to made is subsequent builds).
The 0.2.5 build also has significantly modified music and sound content (implemented in a series of sessions with Adam “Doseone” Drucker and Robert "Dirty Bob" Larder in the week leading up to E3), the new audio with multiple new or revised music tracks for most stages, 4 additional character voice sets, and numerous additional contextual audio events (that trigger sound effects when specific situations occur). The playable stages in the “unstable” build are still experimental but are now sufficiently performant for testing and for us to collate suggestions and feedback on gameplay and performance issues through the Early Access forums (there will be additional optimisations and modifications made in subsequent builds). To start the feedback process we plan to make a series of monitored forum posts (in the next few hours and over the coming weekend) with information on planned revisions, current issues, potential optimisations, and other identified modifications we expect to make to specific stages, game modes, and gameplay mechanics. Specific Information re: head-butts and dropkicks will be posted as individual threads in the Early Access forums in the next few hours.
Information on the new "chutes", "elevators", and "towers" stages and the completed and planned work done on modifying (or remaking) the "buoy", "incinerator", "subway", "trucks", "vents", and "wheel" stages will be posted as a series of individual threads in the Early Access forums this weekend (and in the coming weeks).

List of additions, modifications, and fixes made in the 0.2.5 “unstable" build