The Ticks develops a cold and a new neighbor named Thraggazor, an alien from Diminesion 14B come to take over the world with an army of Tick clones. So first he captures Arthur and clones him(whcih is ridculus, since the clone doesn't even look like him) so he can get a tissue sample of the Tick to clone. Eventually he gets a cleanix that that the Tick snezzed on and takes it back to Thraggazor to create a clone of the Tick made intierrly out of mucus. This is probably one of the most known episode of the entire series. I love how the Arthur clone is green and can only say "I Arthur" and the Tick actually buys it.
Evil Arthur Clone: "I Arthur."
The Tick: "Yes I know, and I Tick."