Blackadder: Back & Forth

When three high-school friends invent a time-machine, they decide to use it to go back in time and prevent other youngsters from making humiliating mistakes.

After a high school lab experiment goes horribly wrong, Mordecai and Rigby must go back in time to battle an evil volleyball coach in order to save the universe — and their friendship.

Ba'al travels back in time and prevents the Stargate program from being started. SG-1 must somehow restore history.

Agents J and K are back...in time. J has seen some inexplicable things in his 15 years with the Men in Black, but nothing, not even aliens, perplexes him as much as his wry, reticent partner. But when K's life and the fate of the planet are put at stake, Agent J will have to travel back in time to put things right. J discovers that there are secrets to the universe that K never told him - secrets that will reveal themselves as he teams up with the young Agent K to save his partner, the agency, and the future of humankind.

Ben, Gwen, and Max must stop an extraterrestrial who plans to open a gateway that leads to an alien invasion.