Tasigur, the Golden Fang
A slightly cheaper Gurmag Angler with an extremely useful ability for grinding out long matches. A more powerful version of the deck runs 2 Tasigur over the Skaab Ruinators.
Better Manabase
An expensive manabase goes a long way in Modern. First off, the deck runs MUCH smoother with a full playset of fetchlands (I recommend 8 to 10). Fetchlands are important because they thin your deck of lands, making your Mindshrieker pumps much more consistent. They also boost the power of your Anglers and help shuffle your deck if you decide to run something like Halimar Depths.
Simian Spirit Guide is another interesting and somewhat double-edged mana option, helping you ramp while not being horrible to hit with Mindshrieker off the top.
Training Grounds
An unorthodox option, but one that works really well with Tasigur and doubles the rate at which Mindshrieker can boost up. Just imagine: turn 1 Training Grounds, turn 2 Mindshrieker, turn 3 activate Mindshrieker 3 times hitting three big creatures -- gg. If you end up going with Training Grounds, you could consider trying out Pack Rat as well, a card that can win games by itself and can win even faster with TGrounds up, although you will need a consistent source of black mana.
Kira, Great Glass-Spinner
Mindshrieker's biggest problem is its total weakness to every kind of removal. Kira solves this problem very cleanly while being hard to get rid of itself, and one or two copies could go in over Vexing Sphinx.
Commandeer
A nice one-of, extremely strong against the right deck. You will often have the dead cards in hand to use it to its maximum ability. And of course a 7 CMC card with Mindshrieker is nice.