4th and Forever: Muck City (2020)

S5E1 The Unstuck Man

Following a tumultuous experience, Rembrandt and Maggie discover that Colin has vanished without a trace. Their concern deepens when they encounter a mysterious individual asserting he is Quinn Mallory. As Rembrandt and Maggie unravel the truth, they realize too late that they are entangled in a sinister scheme orchestrated by a malevolent genius intent on preserving his own existence.