Homer discovered the Daybreaker’s aftermath

“I may be the first non-Brazillian person to travel through time.”

*(Accidentally kills off dinosaurs with a sneeze)  
“Oh man, this is gonna cost me.”

“Oh, I wish, I wish I hadn’t killed that fish.”

Yup, this is the particular example that came to my mind when I saw this episode.
 
I wonder what would be the thing that resulted in the super good future with the donut rain.
 
Would need to seem super bad and drastic in the past but ultimately have the best result…
 
Perhaps Twilight tris to reflect a “blast and incapacitate full grown mare” spell but when it bounces it heads for Rainbow and a bully. Fluttershy suddenly and with great skill and speed weaves past the other bullies and intercepts the hit and gets blasted off the cloud at terrifying force.
 
At this point Twilight gets sent back and encounters… Not sure.
 
 
But what did happen after she left was that the animals not only saved Fluttershy but also tried to tend to her wounds before they were scared off by the sonic rainboom caused by Rainbow, then even while still injured she works to comfort the animals.
 
This, along with how she got blasted help cement some courage and determination into Fluttershy.
 
Rainbow, after taking a command role and instructing two of the bullies to calm the other children down and the third to go get help headed down at incredible speed to go find her friend dispite the possible dangers.
 
This not only bring out bravery in Rainbow but also jump started her responsible and leader type side not to mention bringing out nurturing and responsible sides in the bullies who just moments earlier had also witnessed Fluttershy’s courageous and selfless acts.

….  
DOH!!!

He would later encourage Ponyville to grab any and all firearms to shoot a bunch of zombies.

“Don’touch anything?! I’ll touch whatever I feel like!”