They may share a theme or card type, feature art by the same artist, or be special collaborations
This time around, Amass Orcs is representing the vast Orcish armies of Sauron and Saruman within The Lord of the Rings universe, but it is essentially the exact same mechanic (and has been errata'd as such): Amass 1 would get you a 0/0 Zombie Army with one +1/+1 counter on it, Amass Orcs 1 would get you a 0/0 Orc Army with one +1/+1 counter on it, unless of course you did both, in which case you'd have a 0/0 Zombie Orc Army with two +1/+1 counters on it
UW Blink is a deck that's all-in on flicker effects
Theyre printed with the same art, frame, set symbol, and collector number as when the card was first printed except with a planeswalker symbol in the lower-left corner , just like Mystery Booster cards
This gives you a reliable way to cast Reaper King, though youll have to restructure your deck to meet its companion requirements
Vaevictis Asmadi, the Dire can definitely be a great Jund commander for a chaos deck