I think there is a bug in the Hastur Mythos Effects in the iPad HD version of Omens.
Playing a game just now, two midnights in a row, the Hastur Mythos effect displayed the monster icon, but no monster title. The monster icon flew up into the HUD area, as usual, but the monster total did not increment, and the message "a monster appears!" was not displayed.
I had 8 monsters out already, and thought it might have something to do with a limit, but the doom tokens added monsters as normal, pushing it up to 10 monsters out.
I can't explain what's going on here. If there is no Mythos effect, the game always says so.
When the monster icon appears for the Mythos effect, the name of the monster also appears, like "lunatic" or "high priest" .
Until today, I'd never seen the Mythos effect show the monster icon and have no monster name displayed. Perhaps there is a hidden limit to the number or kind of monsters Hastur's effect can place, and so nothing was added because they were already all out on the map?
I'm not sure, but it was confusing enough that I think you ought to check it out and put in some kind of message so the player knows what is happening.