My problem is that I want to play these cards (I have them online!), but I have immediately faced hate for playing them. They ARE unfair. In Just for Fun, most decks can't play their creatures as fast as this deck can. People talk about Eye of Ugin and Eldrazi Temple, but no one has mentioned Thespian's Stage. The new Modern Eldrazi manabase is similar to 12-Post in Legacy. Now you have 8 and possibly as many as 12 lands that are effectively Sol Rings.
Out of nowhere a junk rare like Drowner of Hope is getting competitive playtime! In Standard, it's a 6 drop 5/5. With the Modern Eldrazi manabase, with an Eye of Ugin and an Eldrazi Temple on the board you get a 2 mana discount off the Eye of Ugin and two more mana from the Eldrazi Temple. Now all you need is to come up with another colorless mana and a blue mana. A turn 6 card turns into a turn 4 card. That is a huge difference.
The 2 mana discount from Eye of Ugin has a Black Lotus-like effect. We can imagine opening hands that are just absurd: Eye of Ugin, four Eldrazi Mimics, an Eldrazi Temple, and a Thought-Knot Seer.
Turn 1: Eye of Ugin, Eldrazi Mimic, Eldrazi Mimic, Eldrazi Mimic, Eldrazi Mimic
Turn 2: Eldrazi Temple, Thought-Knot Seer, attack for 16 with the Eldrazi Mimics, and select a nonland card from your opponent's deck and exile it. Now you know your opponent's hand and the game is at 20 to 4. Whatever you draw turn 2 you can't cast and so it does not matter.
Yes, this is a very rare scenario because your opponent should have an answer by turn 2, but it is conceivable. Let's take Eye of Ugin out of the equation. Assume a God hand to be three Eldrazi Temples, four Eldrazi Mimics, and a Reality Smasher. Now even the fastest sequence is not nearly as fast:
Turn 1: Eldrazi Temple, Eldrazi Mimic.
Turn 2: Eldrazi Temple, Eldrazi Mimic, Eldrazi Mimic, attack with first one for 2. Draw an Eldrazi Temple. Now you have drawn all four possible Eldrazi Temples. Game is at 20 to 18.
Turn 3: Eldrazi Temple, now you can cast for 6. Draw an Oblivion Sower. If you cast the Reality Smasher, you can swing for 15 with the three Eldrazi Mimics, and 5 more with the Reality Smasher because it has Haste. If you cast Oblivion Sower, you are hitting for 18. Either way, you win if unanswered. Yes, this is also a very unlikely scenario, but it is demonstrative of how powerful even Eldrazi Temple is. Oh, and you scored a few lands from the Oblivion Sower from your opponent (not that this matters, you have already won).
Take Eye of Ugin AND Eldrazi Temple out. Now the God hand is nowhere near as powerful. You have killed off both lands that allow you to cast a turn 1 Eldrazi Mimic. There's no point in laying out a sequence for this case since it will look a lot like other very good hands that can win in turns 4 or 5, and that is OK for Modern since it is possible with God hands from other competitive decks. (Infect and Storm can definitely win in 3 turns if unanswered). But wait, Infect and Storm can win in turn 2.
In order to differentiate between Infect, for example, and the baby Eldrazi deck, we need to look at how an opponent would respond to a God hand from one or the other deck. In Infect you can cast a Glistener Elf and on turn two boost it with four Mutagenic Growths. This is not different than the examples above with Eye of Ugin and/or Eldrazi Temple in that it will be gg. What is the difference, then? The difference lies in the board presence of the two decks. You can hit the Glistener Elf with any number of 1 mana and 2 mana answers in turn 2 (a very long list of removal spells), and you can also counter at least one of the Mutagenic Growths. The problem with the two baby Eldrazi scenarios above is that you can't hit three or four Eldrazi Mimics with a single spell for 2 mana. Therefore, the field presence created with Eye of Ugin and/or Eldrazi Temple and Eldrazi Mimic exceeds that of Infect or Storm. If this wasn't the case, in a field as large as the OGW Pro Tour, at least one infect deck would have made it to the top 8.
It will be interesting to see what happens during the rest of February 2016. It does not seem likely that a new deck will be able to counter the baby Eldrazi deck. Ghost Quarter can kill off Eye of Ugin upon entry into the battlefield, but the other two lands in Modern that can do this, Encroaching Wastes and Tectonic Edge, do so later in the game by requiring an activation cost-4 mana for Encroaching Wastes and 1 mana for Tectonic Edge. In addition, who wants to run from 4 to 12 land hate lands to knock off Eye of Ugin?
Others have mentioned Painter's Servant, but this is a fool's errand. When we find ourselves looking for cards that answer a problematic card, and the only answer is a single card, we know we have a broken format. Is everyone now going to main deck Painter's Servant? I don't think so. If the list of cards that deal with Eye of Ugin was a few dozen instead of a handful, we would not be here. The baby Eldrazi deck could not have dominated the OGW Pro Tour if we had lots of answers against it boosting the baby Eldrazi.
All of the options are not good:
1. Ban Eye of Ugin: that hurts Tron, a major deck in Modern.
2. Ban Eldrazi Mimic: this card just came out. No one wants to buy packs of a new set and pull a banned rare. Imagine if Snapcaster Mage would have been banned right after it came out.
3. Wait it out until Shadows over Innistrad comes out, and maybe that set has some good baby Eldrazi hate (it should, that's how all TCGs work).
My best estimate is that Wizards will use option 1 and ban Eye of Ugin, just as it did with Treasure Cruise and Dig Through Time.
If Wizards wanted to be certain that the baby Eldrazi will not be format-warping now or in the future, there is a 4th option: ban Eye of Ugin AND Eldrazi Temple. There is a small probability that this double banning could happen and I would like it. Otherwise, Eldrazi Temple is effectively a Sol Ring in Eldrazi decks when casting creatures.
Here is the Reddit link: https://www.reddit.com/r/magicTCG/comments/44ohf4/oops_i_think_modern_just_got_broken/
February 12, 2016 update:
Eye of Ugin/Eldrazi Temple compared to Treasure Cruise/Dig Through Time: In my opinion, these two pairs are apples and oranges in one important aspect: Treasure Cruise/Dig Through Time could be added to any deck, even Red Deck Wins as long as you were willing to splash blue. The problem with Eye of Ugin/Eldrazi Temple is that it enables a tribal effect that requires a specific deck. You can't add Eye of Ugin/Eldrazi Temple to Red Deck Wins. This difference is the reason why I believe that Eye of Ugin/Eldrazi Temple may need to be banned sooner than it took to ban Treasure Cruise/Dig Through Time.