If a creature carries a powerful enters-the-battlefield effect or has haste, then players are able to guarantee getting some value by casting it when their opponent taps out
You will still see some Jund players sleeve up a set of Leyline of the Void, but it is also common to see a couple copies of Surgical Extraction, Nihil Spellbomb, and Grafdiggers Cage to cover bases in multiple matchups
6 Etali, Primal Storm Every Barbarian Needs A Dinosaur Friend Karlach means attacking a lot, and Etali loves it when it gets to attack
You also need to be playing a wide variety of creature types in order to receive these counters turn after turn
For example, you will see that many users ask for, say, 8 Battle Style packs in exchange for a copy of Crobat V
Cataclysmic Gearhulk