Here's a view of Cthulhu from the wiki to compare Emrakul's two pieces two (You can find the entry here
Cataclysmic Gearhulk 3WW Artifact Creature Construct Vigilance When Cataclysmic Gearhulk enters the battlefield, each player chooses from among the non-land permanents he or she controls an artifact, a creature, an enchantment, and a planeswalker, then sacrifices the rest
The removal offered by Shriekmaw and Acidic Slime will help with our overall midrange plans, and with the Shriekmaw specifically, I wanted a card that could be cheap rather than expensive
I think Arena uses "perpetually" to track this kind of effect, and this would be a good place for it
Outlaws of Thunder Junction gave us the Greave's at home version in Lavaspur Boots, thankfully the power boost helps offset how much worse ward is as a targeting-deterrent, but it's still several notches below the other two