Tiger was Dee Dee's imaginary friend, Koosalagoopagoop, in "The Koos is Loose", "Koosalagoopagoop", and "Jeepers Creepers, Where is Peepers?".
Keep Circulating the Tapes: Bits of the first season were released on a now out-of-print VHS tape, the same goes for a collection of Genndy's favorite episodes. "Ego Trip" was released only on VHS, and that's out of print as well. The first season did get an official DVD release, but it does not include the banned "Dial M for Monkey" cartoon "Barbequor". Thankfully, the entire series (sans "Barbequor" and "Dexter's Rude Removal") is available on iTunes, and the entire first and second seasons (again barring "Barbequor") are available on Netflix.
Missing Episode: "Dexter's Rude Removal", an episode the crew made for themselves as a joke which contained heavy use of profanity that not even Cartoon Network would find permissible. Before the end of 2012 it had been aired outside crew parties only once, at a Genndy Tartakovsky panel at a convention where they kicked out everyone under 18. [adult swim] released the episode here!