1 Spit Flame
Basically, the first Dinosaur that enters the battlefield in each turn (including an opponents turn if youre being fancy) triggers discover X, where X is its toughness
Even better, your opponent is usually more than willing to help you out by summoning Cyber Dragon cards that you have plenty of opportunities to take control of and turn against their master
This makes it an interesting card that is worth splashing as a 1-of in your deck if you need something that can hit a Pokmon ex hard
All this is in service of killing bosses that are, say, fleshy bags that belch flies at you or goopy meatpiles with devastating barf attacks, until you face your mother, and, finally, your pure mirror image as you appeared before all this nasty stuff happened to you
Hangarback Walker is also an essential element of aggressive artifact decks, and is one of the easier slots to fill if you want to feature Arcbound Ravager in your Cube