Considering that Scarabs start at 2/1, what exactly can they devour? And, while they do grow logarithmically, on average it requires three or four of them to be useful at all, and you can only immortalize one thing per turn, unless you run multiple Anubis or Quintessence. Plus, how are you going to get the Gravity to maintain the Scarabs without adding extra Gravity Towers?
Catch 22 moment: seems to me as if the deck has to go over 30 cards to be effective, but the farther you stray from 30 cards, the less effectiveness the deck has. Based on this, I would like to refute the decision to place this deck in the high tier, unless substantial proof can be shown that it overwhelmingly deserves it. Middle tier seems like a more suitable place for it at current time.
Since the deck uses Time, it can go above the normal 30 cards from extra drawing power with hourglasses. Then, TUs can help scarabs grow faster. You could easily have 3 out by turn 4ish. And if you don't, phase shields can help you stall.
You get the extra Gravity from adding 2 or so extra towers, but the mark is the main thing (by the time you start eating, you'll have 3+ saved up).
In addition, Time/Aether (mark Aether) is useful simply for immortal Silurian dragons. For instance, 5x Silurian Dragon, 3x Anubis, 3x Quintessence, 3x Hourglass, 2x Turtle Shield, 14x Time Tower, Mark of Aether. That's a duo time/aether and, though it doesn't use Scarab/PU, uses the synergy of anubi and quintessences to immortalize those big 14 damage creatures.
