So basically, I'm listing all the Butterfly Effects, that I know of, in Warrior Cats :D

1. Snowfur's Death
Warning - Accuracy may be off

If Snowfur never died, Thistleclaw would've been good, meaning Tigerstar would be good, which would make all those cats live, Scourge would've never come to the forest, I am fairly sure Hawkfrost and Mothwing would've never been born, and that means Firestar probably would've have lost as many lives... And Tigerstar would probably become the leader of ThunderClan.

2. The Dogs

If the dog pack never came to the forest, Bluestar would still be alive, probably doing some hurtful stuff to her Clan...

3. Rusty

If Rusty never came to the forest, the 'Fire Alone Can Save Our Clan' prophecy never would be finished, a lot of stuff would be different, and the entire series would be thrown off.

That is all I know of, as of now, and if any of you guys have some, please tell me :3