This kind of deck has always been one of my favourites in any given format, cube not withstanding. There are lots of ways to go about comboing off, some take infinite turns, some win with storm, some make infinite mana and so on. It is not really that relevant how you actually win just so long as you can (I have played against too many cube decks where a win is never possible for them yet it takes several hours of my time to realise this). The win conditions are typically just one card with a few specific support cards and perhaps a tenuous back up strategy. I did a UR version that used storm cards to win and so just to be different this particular list is an infinite mana combo with Palinchron that uses Brain Geyser for the win with a backup plan of taking infinite turns should the decking strategy fail. I think the storm builds are the most consistent as there is ever more creature disruption in the cube but it is fun to be different! The bulk of all UG land combo decks look the same and are supported by the same core of cards regardless of the actual combo and this is rather different from the other Ux storm style combo decks as green has such good mechanisms to get more lands in play.
The core cards are those from blue that untap lands and those in green that get you more, in addition to this there are the familiar draw spells of choice from blue and some recursion of choice historically from green. These four effects dominate the deck and give it great consistency in redundancy. It is a highly robust form of combo deck as it will not fall to pieces against counter magic and generally stands up well to disruption. Rule of Law effects are direct hosers and require an answer however these cards are typically never played in my cube even in rotissery so the worst you will have to face would be an Ethersworn Canonist. Another unusual facet of this style of combo deck is that you never want to go off early, you want to delay until the last moment, against agro decks this is the turn before you are in range and against control typically when they invest a big chunk of their mana in a threat although the turn before they kill you with it is also an option. Every turn you delay will increase your odds of going off and being able to win and so judging how long you have to set up is one of the more important aspects of playing these decks.
Sakura Tribe Elder
Helm of Awakening
Heartbeat of Spring
Fact or Fiction
Simic Growth Chamber
Force of Will
This list is a fairly robust one with two Heartbeat effects and two ways of reducing the cost of your spells. It also has a main deck Moment's Peace which doesn't aid the combo at all but buys a lot of extra time against most decks. What this list does not have is counter magic but then it doesn't really need it. Abeyance is going to be more useful at doing what you most what from any counter magic and isn't really needed any ways as you tend to be so effective at out drawing and out mana producing control decks. You are weaker against decks with less disruption and a faster clock than combo decks tend to be hence playing Moment's Peace where one might expect counter magic. The Capsize is also not at all helpful in the combo but serves as your one out against things you can't beat which is somewhat of a must have when you can't rely on Wishes. Capsize is usually the best choice for an out in this kind of deck as it becomes quite a serious threat when you reach the point of having loads of mana to throw about.
Time Walk effects are surprisingly good in these kinds of decks, even the pure storm ones oddly. Often you start to go off and get loads more lands in to play and could carry on and likely take the win however will be in an even better position to take the game with another draw and untap step. In this particular build I would be happy playing two Time Walk effects, even both at five mana, if I could reduce the overall mana curve a bit. These decks typically do have quite high curves and can get some very awkward opening hands and so cheap card quality spells are very useful, both Brainstorm and See Beyond are well worth of inclusion, even with Brainstorms lack of synergy with Helm and Familiar. The most cuttable top end card is the Mind's Desire which is very powerful but somewhat cumbersome and random, it is nice to have the option of throwing it out there with four storm and hoping to blag a win when all else looks doomed but compared to Time Spiral it is underwhelming and non-essential, even in the pure storm builds, although obviously it is better there as it helps to generate lots of storm itself.
I have less ramp than you might expect in a deck like this with only Tribe Elder, Harrow and Nature's Lore representing. I cut the Explore from my list at the last minute for the Capsize when I realised how vulnerable the deck was to certain cards. The Explore had to go as I was being greedy on lands and playing 16 instead of the far safer 17. I played the Simic Growth Chamber because it has OK synergy with the untap land effects in the deck and goes some extent to counting as an extra land in the list however it is somewhat of a risky play and should just be two land versus decks with land destruction. Tribe Elder is great because it is a real aid against the tempo decks which are your hardest matchups, the Nature's Lore and Harrow are ideal because they can actually generate quite a lot of mana when you have the right effects in play and therefore really help combing off. Normally Lore costs two and leaves you one extra mana once cast and Harrow is the same but costs three and generates two. Once you have both a cost reducer and a land production doubler you will pay one for Lore and generate two and pay two for Harrow and generate four, all the while increasing your land count. Harrow is doubly good in the pure storm decks as it is instant and those decks are able to combo kill at instant speed when needed. The Time Walk effects also double up as pretty decent Explores when you get to five mana and are not at all wasted when used in this capacity. Playing the basic plains is also a bit dodgy and is only really in there so that Tribe Elder and Harrow can fix for white, usually you will want to be sacrificing it to the Harrow however!
Sunscape Familiar and Helm of Awakening are the two reducers in the deck and come with their own pro's and cons. The Helm is easy to cast however it is symmetrical and thus very scary to tap out and cast on turn two. The Familiar however only effects you and provides a reasonable defence as well in the early game. Now a days it is easier to kill the Familiar and it does also require you to slightly weaken your mana base in order to reliably cast it on turn two. They are not essential to the combo but enhance all your other spells and make setting up for the turn you want to go off easier as well as the turn in question. A healthy balance of land rampers, cost reducers and land production doublers provides the most effective overall mana explosions. Heartbeat is pretty essential in the deck, hence the name of these UG combo styles however Wake is not needed. It is safer to play but not overly as it costs so much more. Generally you have to tap out to lay Wake and hope you survive passing the turn so you can win on your next, with Heartbeat you tend to cast it a turn earlier then use the extra mana left after to cast something like a Harrow or a Frantic Search so you can go off that turn. As such I have played many a deck with only Heartbeat in this slot and relied on tutor effects and more card quality to find it.
Gifts Ungiven and the recursion allow you to tutor for the specific things you need to go off with or win with however it is quite slow to do this if it is prior to going off. Both however are still useful in their own right while setting up or going off and although the Gifts is not 100% essential the recursion is in the singleton format even with reasonable redundancy of your effects. Palinchron and Braingyser provide the kill in combination, the Palinchron generates infinite mana with a Heartbeat and six lands in play which is useful enough while going off and then allows you to guarantee a Geyser kill by forcing them to draw all their cards and more. When it can't be used to kill it can be used to draw a decent chunk of cards which is why I prefer it to Stroke of Genius, the extra card you can get on turns three through five in the early game is huge.
Time Spiral and Timetwister are also pretty huge in the deck, you do not need both but they are the most cards you can draw for the mana in blue as well as allowing you to reuse your cards and carry on going off perpetually in the case of Twister (with the recursion). Time Spiral is the perfect card for the deck and although you cannot continually abuse as it self exiles it is so powerful that you rarely need to cast it more than once. All the deck really wants to do is untap lands and draw more cards for which this does both in great quantities. Frantic Search is the smaller brother of Time Spiral and also does exactly what you need it to in a place on the curve where you are most grateful for it. If I could not get both Spiral and Frantic Search for my deck I would probably abort the strategy and go for something else.
Some of the cards that I didn't include in the main list but gave as possibilities are interchangeable with cards in the main list, others are most awkward to include. Explore has been discussed, the countermagic fits in the deck in the few slots available for Moment's Peace and Capsize, the cheap cantrip counterspells tend to be best as they can tenuously replace things like See Beyond. Remand has some nice applications with storm mechanics and Denial can be used as a pure draw spell if desperate. Force of Will is a counterspell I do not much like in the deck, it offers great security but is a hindrance to going off, rarely can you afford to exile a blue spell and still have what you need to get it done.
Garruk Wildspeaker is cute in the deck and acts as decent continual and personal ramp while also being an OK win condition however at a cost of 4 he is a touch clunky. Rude Awakening is in much the same vein as a Garruk, more effect but slower and only as a one off. Brain Freeze is an alternate win card and can replace both Geyser and Palinchron however doing this would make for a subtly different deck for which I would make several other slight tweaks (probably to include remand among others). Freeze is totally dead until it is your win card, both Palinchron and Geyser have uses before that ultimate stage and so are better in that respect. Snapcaster Mage I have not had a chance to really put to the test in these archetypes, the exile side of things is a little frightening and the inability to fetch back lands and early permanents also makes it somewhat of a weaker early draw than other recursion options. Despite this the raw power of Snapcaster probably still makes it a very good choice for these archetypes.
The thing I love so much about these decks is their ability to pull a win seemingly out of thin air. You get the games where you phaff around trying to go off and just die before doing anything, you get the ones where you seamlessly go off and win without your opponent ever really effecting you and they are more fun than the first but not exactly great magic, especially for your bored opposition. The games that make this deck awesome fun to play are the ones where you get your hand torn to bits by discard, then a number of your permanents destroyed and you are desperately trying to stay alive while trying to reassemble the broken bits of your deck. You have no relevant cards left in hand if any and just lands in play when you rip a Spiral or a Gifts and take total control of the game all in a few turns of clever set up and explosion.