I'd like to see ability cost upped to 2
AND removal of Shriekers as a standalone card.
Shriekers are not whats overpowered. Graboids are. But graboids are not really a creatures on their own, they are just a way to get a cheap strong attacked called Shrieker.
Think about it. You pay something at turn1, get something untargetable, but mostly ignorable, and at turn2 you get the REAL creature that is not just strong attacker, but also can become untargetable at will. Basically, you can get 12 of those creatures, while paying full price for 6 of them, and part of the price for other 6.
The only similar creature in the game is Fate egg that costs the same amount of quanta to play, but IS targetable, have same cost for "upgrading" it to something else, but that something else is out of your control and can be complete crap, thus not entering into "12 same cards per deck" category.