Not counting troops type units.
Tau have the Riptide
Eldar have Wave Serpent Spam
Grey Knights have the Dreadknight
Tyranids have Flyrants and Tervigons
Chaos has the Helldrake
Imperial Guard have the Vendetta
Demons have the flying Monstrous creatures spam
I look at my marine brothers and don't see any auto includes. A lot of units that are useful in many roles but no unit that see's every single list. Nothing you just feel like you have to buy.
Anyone have an Auto include? I used to always include Sternguard in every list but looking at the new book their use has been slightly less important.