This rather dark clip is from a film called The Adventures of Mark Twain (1985) and is a "feature-length Claymation fantasy [that] follows the adventures of Tom Sawyer, Becky Thatcher, and Huck Finn as they stowaway aboard the interplanetary balloon of Mark Twain. Twain, disgusted with the Human Race, is intent upon finding Halley's Comet and crashing into it, achieving his "destiny." It's up to Tom, Becky, and Huck to convince him hat [sic] his judgement is wrong, and that he still has much to offer humanity that might make a difference. Their efforts aren't just charitable; if they fail, they will share Twain's fate. Along the way, they use a magical time portal to get a detailed overview of the Twain philosophy, observing the "historical" events that inspired his works."

Plot summary is from IMDB