A combo that gives infinite turns without any colour support needed is Prototype Portal + Ugin's Nexus + any sac out let that lets you sacrifice your copies of the Nexus.
You might want to reread Ugin's Nexus they thought of this stuff when that card was designed.
They're saying to create and sacrifice a token Nexus, so that you don't control one when you would take the extra turn.
Two Score, Minus Two or: A Stargate Tail
(Image by totallynotabrony)