Quick update on my testing:

Mouth of Ronom
As expected, Mouth of Ronom was cut. The card is nice, but there are better lands to play instead. The activation cost is too steep, but what set me off the most is that there are simply better ways to get rid of Gaddock Teeg. I do think my paranoia for Gaddock Teeg is appropriate, since Gaddock Teeg is very strong against U/W Miracles as well. That said, after sideboarding in Grafdigger's Cage / Cursed Totem, Maverick isn't much of a deck anymore. We can also ignore Gaddock Teeg by siding out Karn Liberated and boarding in Cursed Totems. Another cool thing is that Godo ignores Maze of Ith, should they have found that land.

Phyrexian Metamorph
Still requires more testing.

Taurean Mauler
Didn't have time to test yet. This card reminds me a great deal of Magus of the Moon though. Magus has disruption, while this is simply a 'dumb' beater. My initial feeling is that Moltensteel Dragon is better at dumb beats.

Arcum Dagsson
Didn't have time to test this yet, but I am looking forward to it. I want to try either a full on Forgemaster combo deck or splash in an UR-build. Probably not enough creatures to support it, unless I play Mishra's Factory or something.