I discovered the Leyline of Singularity deck concept when playing Forge. I felt the potential and coolness of this idea, and transformed it into a real powerhouse far different from the original.
The original deck was 5-color, which meant issues getting the right colors at the right time. The other major problem was the choice of cards didn't go nearly far enough to exploit the legendary rule enforced by the eponymous Leyline of Singularity.
I addressed these issues and created a monster deck that was flexible, consistent, fast, and competitive. First I winnowed the deck down to 3 colors in order to access a consistent mana base. I also powered up the deck with moxen and black lotus. Then I went along with the legendary theme and chose the best legends for the roles. Legends generally had unique, powerful abilities for any given mana cost. The leyline caused every nonland permanent in play to become legends anyway; so my true legends had the advantage over nonlegends.
The final colors chosen ultimately determined what legends and other spells could be included in the deck. And those colors were determined by the key spells that glued together the main concept. Namely Leyline of Singularity, Captain Sisay, Empress Galina, and Karakas. Together they fall under blue, green, and white. Which was great because these 3 colors work very well together to cover a wide range of both offensive and defensive strategies, options, and card advantage.
Besides artifact ramp, I also added low CMC ramp in the form of creatures. These are all green from 1 to 3 CMC. The entire mana base will allow easily casting high CMC legends and spells for their unique devastating effects. Most legends start at CMC 3 anyway, but I still want to play things starting from the first turn. I also added manlands later on, to have a backup plan in case I get mana flooded.
The first legend that I wanted was Thasa, who was always dominant as the centerpiece of standard during Theros. Scrying every turn for free is awesome; she becomes a threatening late game finisher as 5/5 indestructible unblockable god. All that for only 3 measly mana--what a steal. In order to toggle her as creature, I surrounded her with friends like Vendilion Clique; Kira, Great Glass Spinner; Edric, Spymaster of Trest; Jace, the Mind Sculptor; and Nightveil Specter. Coming out of the sideboard, we also have Teferi, Mage of Zhalfir with a whopping 3 blue mana symbols, and other creatures that are blue or half blue.
As such the colors are heavily skewed toward blue. Nevertheless the mana curve toppers are actually green and white. Primeval Titan of course also dominated standard during its heyday. 6/6 for 6 with two additional strong abilities is great deal. However note it is not a legend, but it sure feels like one. The other white finisher is none other than Elesh Norn, Grand Cenobite. She is ridiculously one-sided, simultaneously strengthening your own creatures and weakening your opponents' creatures. Moreover small creatures will even cease to exist while Elesh is in play. Thanks to ample ramp and Black Lotus, 6 and 7 mana aren't that difficult to achieve in this deck.
This deck is actually a toolbox archetype. That means it covers a wide range of cards suitable for various situations that can be fetched from the library on an as-needed basis. The cards that can fetch other cards are Captain Sisay, who finds other legendary cards, not just creatures, but she can also get legendary lands (Karakas), planeswalkers, etc. Then Eladamri's Call can retrieve any creature for only 2 mana at instant speed. Finally Enlightened Tutor will find any artifact or enchantment and put it on top of the library, waiting for your next draw to put the card into your hand. Note this can also get Thasa, which is an enchantment. Thus later I found room for few other gods like Nylea and Kruphix--all the gods can be fetched by all 3 tutor types mentioned here.
Being a toolbox means this deck can transform and adapt to different strategies and styles against different opponents. If you want fast aggro that can kill in a few quick turns, we have cheap yet big creatures for their mana cost. Bank-breaking Tarmogoyf, Knight of the Reliquary, Rafiq of the Many, Geist of Saint Traft, and other efficient creatures. Stack the deck with creatures at 3 power for 3 mana and go to town.
If you need to hose and suppress other broken strategies, then GWU are perfect colors to do so. Against oppressive artifacts and enchantments, try Kataki, War's Wage; Aura of Silence: Aura Shards; Ray of Revelation; Glen Elendra Archmage. Against aggro, the maindeck strategy already can handle most of them. Kitchen Finks grants extra life and even returns after dying to do it again. If infect is an issue, bring in Melira; she also combos with persist, so the Finks and Glen Elendra will keep coming back to play over and over again. If you still have trouble, slap down a Michiko Konda, Truth Seeker to try to slow down the opponent. Against combo decks, perhaps put in counterspells and Teferi to stop their shenanigans. Even consider Dovescape stop decks that win with noncreature strategy.
Singularity Natural Order