The full texts of these abilities are At the beginning of the monarchs end step, that player draws a card and Whenever a creature deals combat damage to the monarch, its controller becomes the monarch. There are several cards with abilities that trigger depending on whos the monarch
The beginning player, though, doesn't tend to think of the death trigger as a result of blocking, so the idea that you could combine the creature damage with the death trigger effect never occurs to him or her
Eventually you get enough copies in play to then finish the chain by copying Goblin Recruiter once more to put Sling-Gang Lieutenant on top of the library to then sacrifice all your new Goblin friends to kill your opponent
The December preview gave us a pretty good idea of what to expect for this collaboration
Black Being able to bring a planeswalker back probably makes the card playable
I still think that if you were big on the tribes featured on Ixalan, this set is great, if not easily skippable