Scar's plans for Mufasa and Simba are revealed while Scar went to yell at the hyena's for not killing Simba when they had the chance. Scar developed an elaborate plan to kill both Simba and Mufasa so he could rule over Pride Rock instead. And he uses the hyenas to do so by creating a stampede.
Scar tells Simba to wait on this rock while he gets a "surprize" and tells him to work on his roar. Simba does so, and then a stampede starts and he thinks he started it by his roar. But actually the hyenas did.
Mufasa and notices that the wilderbeast heard was on the move, but did not know that Simba was in the middle of their path.
Until Scar tells Mufasa.
Mufasa rescues Simba in the middle of the stampede, but gets into a little trouble himself trying to get back up the cliff.
OF course Scar helps Mufasa fall back down in the middle of the stampede to be trampled over.
Simba rushes down to see his dad after the stampede passes, but his father has already died.
Scar lets Simba believe that the stampede was all his fault and blames Simba for Mufasa's death. Simba is so upset that he runs away. Scar sends the hyenas after Simba to kill him, but they don't get the job done. But Scar, believeing that Simba is sucessfuly killed, goes back to Pride Rock and declares himself the new King because both the king and his sucessor died.