The first known thing about asdfmovie is that Tom originally created a character called asdfman. Tom said in his asdf origins video that he got the asdf in the name by slamming a keyboard.
The series would go on to be extremely popular since the 4th installment, with many animators and guest voices leading the way of the popularity. There was a song in the 10th installment called "Beep, Beep, I'm a Sheep!" Which went on to be really popular. Getting a comment edition, a remix by The Living Tombstone, and even one of the special songs in Just Dance 2018.
The "I like trains" kid
A boy who can only say "I like trains". Whenever he says this, a train appears. There is a song about him 
The "Do the Flop" Guy
A man who invented "The Flop", which is a dance move consisting of falling face-first on the floor. When he says "Everybody do the flop!" everyone does the flop. He also has a song 
A turtle with a button on his shell. When the button is pressed, he explodes. There is a song about him 
A muffin who expresses a desire to die/be eaten. Phrases include "Why won't you let me die!", "Somebody kill me!" and "It's muffin time!"
Muffin Time is an Asdfmovie themed card game, announced on August 14, 2019, in a video uploaded by TomSka. The video also explains the rules of the game. It was published by Big Potato Games, and has 200 unique cards.