The Fan Game - Back to the Future Part III: Timeline of Monkey Island

Marty finally gets the almanac, leaving Biff to crash into a manure truck.
As Doc hovers above in the time machine; Marty burns the almanac, reversing Biff's changes to the timeline.

Then later a portal opens and sucks the car into it before Marty can join him on the time machine.
A few seconds later, a member of the Guild of Weavers appears bringing him a message: "The timeline has changed! Doc was transported back to 1655!" “Largo LaGrande” attempted to save “LeChuck” with a voodoo temporal spell. Wrong target.”

Bobbin Threadbare gives him a map describing where the DeLorean time machine is located.
The Map mentions that located in the DeLorean are instructions on how to repair it, using 1955 components, so that Marty can return to 1985.

Dr. Emmett Brown is shocked to see Marty moments after sending him back to 1985 and he faints outside of the Hill Valley Courthouse.

After they recover the DeLorean inside a cave in the Caribbean, they discover a tombstone bearing Doc's name that states that he died on July 3,1655.

The tombstone also reads that Doc had been “Shot in the back by William "Dogfish" Tannen, over a matter of eighty pieces of eight and was erected for him “By his beloved Carla, the Sword Master of Mкlйe Island". Marty decides to go back to 1655 to rescue his comrade.