From Homestar Runner Wiki
In the Strong Bad Email highschool, Strong Bad took a guess as to what the Homestar Runner gang was like back in high school. This page elaborates on how Strong Bad remembered what the characters were like in their teenage years. It should be noted, however, that Strong Bad himself admits that he has "an extremely unphotographic" (or "doodle") memory, and it is therefore uncertain to what extent these recollections are accurate.
 Teenage Homestar RunnerHomestar Runner. He appears on the show The Homestar Runner Mysfit-steries with his friends Marzipan, Strong Bad, and Strong Mad, all in their teenage years. Strong Bad and Strong Mad were frequently trying to get Teenage Homestar out of his stripèd pants. He also has his friends play in a band, just in case; he himself plays guitar (left-handed). He is similar to Fred on the show Scooby-Doo.
 Teenage Marzipan
Teenage Marzipan is Marzipan in high school. She and her teenage friends Homestar Runner, Strong Bad, and Strong Mad are on the show The Homestar Runner Mysfit-steries. She can play the tambourine, and does so in the gang's band. Teenage Marzipan looks like Daphne of the show Scooby-Doo, and uses a similar catch phrase, where Teenage Marzipan's is "Stampers", Daphne's was "Jeepers". In contrast to the normal, "adult" Marzipan, this teenage persona features a nose and visible human legs.
 Teenage Strong Bad
Teenage Strong Bad is what Strong Bad was like in high school. He is on The Homestar Runner Mysfit-steries with fellow teenagers Homestar, Strong Mad, and Marzipan. He plays keyboard in their band, despite having boxing gloves for hands. He and Strong Mad are always trying to "liberate" Homestar from his ridiculous stripèd pants. Strong Bad appears to have the slumped stature of "Shaggy" from various Scooby-Doo television series. Also note that his hat bears the color of Shaggy's green shirt and reddish pants. He doesn't believe in "mysterious". He also is wearing a recolor of the hat regularly worn by Coach Z.
 Teenage Strong Mad
Teenage Strong Mad is Strong Mad's teenage version. He is on The Homestar Runner Mysfit-steries with Homestar, Strong Bad, and Marzipan, all in their teens. He and Strong Bad are always trying to "liberate" Homestar from his ridiculous stripèd pants. He looks very similar to Velma on the show Scooby-Doo. His singlet has a lowercase "m" and a period. Unlike his modern day counter-part, he appears to have more fat than muscle.