From DariaWiki
J.B., after his narrow escape in "Through a Lens Darkly"

An intelligent talking bulldog who appears in the fanfic, "A Hard Days' Night." He is supposed to be the same brown brindle bulldog that was almost run over by Daria at the beginning of "Through a Lens Darkly." J.B. (his initials probably once stood for John Bull) is the pet of Dawn, a background character in the Daria show, but he has a secret life combating dangerous and extraordinary forces attempting to destroy or conquer Lawndale. His partner in such battles is his universe's version of Andrew Landon, a mathematics genius who commands a squad of crimefighting teenage boys (the Irregulars).

A brindle bulldog also appears at the end of "That Was Then, This Is Dumb," chasing after the Yeagers' yellow VW, but that one has white patches instead of light brown patches.

Could this be J.B. in "That Was Then, This Is Dumb"?