This might be due to a spell or ability resolving, a permanent you control entering the battlefield with counters, or combat damage from a source with toxic, infect, or wither
The original's already been heavily meme'd on due to its verbose rules text, and squeezing all of that onto the poster version is headache-inducing
The smallest Planeswalker flirted with a $90 price tag and was splashed into all kinds of off-Blue decks, facilitated by a format of fetch lands
The Earth King is at its best when you can curve a cheap 4-power creature into it, perhaps Surrak, Elusive Hunter in Standard
If we play it as the last card in our hand, we can easily spend our next several turns dumping mana into it rather than letting our mana go to waste