TLDR
Try to get all basic lands into play and swing for the win.
This is just a brain child at the moment, vaguely inspired by Mons from CEDH TV where he runs Valakut, the Molten Pinnacle and Manabond inside Thrasios/Vial Smasher. Now, this is far from CEDH and can never be. Thrasios, Triton Hero by himself is just better in almost every way. Anyway, when I put this idea into paper I'll see what to cut or add. Of course, suggestions are always welcome, but I take into account budget and other decks I own. I'd like them to have not too much overlap.
The overall strategy
I want to establish right away that this is not a landfall-trigger deck, primarily or necessarily. I've got a Omnath, Locus of Creation deck for that. So, all combo's and synergies with Retreat to Coralhelm based on infinite landfall triggers are out, as is the Tatyova, Benthic Druid + extra turn spells strategy. The goal of this deck is to get an insane amount of lands into play. We then transform those lands into creatures and attack. That should lead to our victory. Let's take a quick look our commander before we theorise how to achieve that wincon:
For only two mana, we get a 0/4 body with an activated ability. 4 toughness is very nice as it bypasses quite a lot of damage based removal and we can use her as a blocker, especially against early game threats. Since our main source of card advantage is going to be Gretchen herself, we must consider how to reliably get her into play and produce the mana needed to activate her ability. This already highlights on of the prime reason she's not that strong: She needs coloured mana. On the flip side: Her ability can give us extra lands, which serves for more activations down the line. Now, since we rely quite heavily on her, we could run the staples Lightning Greeves and Swiftfoot Boots. Be sure consider to include those if you regularly run into players that have bad threat-assessment and kill her off just because they have nothing else to do, only to find they wasted their removal and now paved the way for something else. However, re-casting her will still be relatively cheap, so it might not be even required to protect her all too well. Both her casting cost of {u}{g} and her ability {2}{u}{g} force us to play a certain balance of lands. Yavimaya, Cradle of Growth is added for a little more consistency for green, but we can't rely on that alone for green mana. Feel free to exclude it. Having said that, the more expensive fetchlands and dual coloured lands will certainly improve this deck to an extent, but Scouting Trek is a nice excuse to stick to basics.
Our spicy value engine:
Gretchen Titchwillow + Biomancer's Familiar + Lotus Cobra
Biomancer's Familiar reduces Gretchen Titchwillow's cost by two, making it {u}{g} to draw a card and put a land into play. We put a forest into play, which comes into play untapped. Lotus Cobra triggers and adds {u} to our pool. Tap the forest that just got into play for {g} and with the {u} from the Lotus Cobra we can draw a card with our commander again. Of course, if we put an island into play, we choose to take a {g} from Lotus Cobras trigger. The nifty thing is, both creatures are of 2 mana value, making Uncage the Menagerie a pretty good tutor. And because of this, Spellseeker has another great target besides counterspells, adding to its usefulness and versatility. I don't think I'll be adding Spellseeker, though, due to its IRL cost. The same goes for Training Grounds. It currently is in this decklist, but I don't own a copy. It's mainly there for goldfishing and testing.
The absolute bombshell will be this card, however: Scouting Trek. With all 3 creatures in play and this 2 mana sorcery, we are able to dump all basic lands in our entire deck onto the battlefield, and will still guarantee land drops if we somehow need or want a specific number of lands on top of our library and we don't have the creatures out.
Or straight from the latest set:
Scouting Trek > Cultivator Colossus
Abundance > Cultivator Colossus.
All lands with Cultivator Colossus come into play tapped.
Just using Abundance with Gretchen Titchwillow is a nice engine. If we don't truly combo off with these two cards together with Biomancer's Familiar / Lotus Cobra, it is still a moderately powerful value engine.
Don't be too hasty to bring your commander out to play. If you have the option to Three Visits on T2, I'd do so over playing Gretchen Titchwillow. Our commander only adds value to our plan if we have the mana to activate, so ramping with spells is most of the time much more beneficial. Of course, if you're low on cards, this might change.
We go to combat
Now, we need to go to combat with our lands. Here's how we can go about this:
Jolrael, Empress of Beasts is out due to the steep combined cost and sorcery speed, but we keep Kamahl's Will and Sylvan Awakening can turn our lands into a huge army. In a pinch, Kamahl's Will can be used in a defensive manner (and later recurred with Noxious Revival).
In your end step...
One of the problems we face by having combat damage as our wincon, is that our creatures will not have haste (unless we use Sylvan Awakening). This means that, ideally, we like to activate Gretchen Titchwillow at instant speed, just before our turn. This server two purposes: First, we hold open mana for interaction like counterspells/bounce/spot removal. Second, all our lands we turn into creatures on our own turn won't need haste; they were already in play before our turn. Note that if someone wants to remove one of these combo pieces, we can just respond to their interaction by activating our commander - we can just keep putting Gretchen Titchwillow's ability on the stack as long as we have mana available. We might draw into some counterspell and can ramp into more lands, making it more likely we can actually play those spells right away. Chord of Calling deserves to be mentioned here. Although the convoke clause on this card doesn't make sense at all in this deck, it's still a 5 mana value instant-speed tutor for a creature of 2 mana value, directly to the battlefield. Summoner's Pact, a 0 or 4 mana tutor, needs a little thought to played correctly, as to not lose the game, but can enable a very strong turn. Because instant speed is so nice for combos, we consider Alchemist's Refuge as a land.
It's possible we won't be doing much during our own turn in terms of attacking. We run few creatures and most of them cost much mana. We likely won't be attacking during most of the early and mid-game, the only thing we'll do is invite others to come attack us by having no board presence. An enchantment that's worth considering, is Defense of the Heart. Shouldn't be too hard to trigger. Getting both creatures (again, Biomancer's Familiar + Lotus Cobra/Tireless Provisioner) into play, we only need our commander and our engine is set up. This might deter others from playing more creatures, if they know how much value we might get if they over-extend. All the better that it is a trigger, making it much harder to respond to than a spell.
Keep expanding
Getting your Seedborn Muse to stick is going to provide you with loth of value. Muddle the Mixture is another absolute banger in this deck. A spell that can either protect us from boardwipes or tutor for one of our 2 mana value pieces. Fantastic!
Notable exclusions:
Reliquary Tower - Not a nonbo with the Manabond per se, but another land that doesn't gives us either {g} or {b}, which I don't like. After cutting Treasure Hunt the necessity for this land is ever further reduced.
Treasure Hunt - We have too few tutors for this card, as we need our tutors for another piece of the combo, Scouting Trek. Also, we have no easy way of getting all our lands from our hand in play, aside from Manabond, another card which is cut.
Manabond - We have no tutors for enchantments, making this card way too situational for consistent play.
Zendikar's Roil/Rampaging Baloths - The first is a personal favourite of mine, but have to cut it due to too high mana value and mostly, uniqueness of deck/flavour.
Roil Elemental - Too expensive. Would love to play it, but rather have more consistency for our main combo.
Cosima, God of the Voyage
- Card draw based on land drops. We do the opposite thing, we only get more land drops if we draw more cards. It feels like a 'win more' card, which doesn't actually help us win.
Final thoughts
So, having covered most of what this deck is about, here are my final thoughts on this, as of yet, unfinished decklist.
First off, I understand very well that this commander is ahem... cough *trash*. At the moment of writing, EDHREC has 148 decks with Gretchen Titchwillow at the helm. However, I don't want to purchase Thrasios, Triton Hero. Just too expensive. But I still want to try out how I, as someone who usually hates winning/playing by beats, can build this commander to something that fits my style of playing, which is combo. (This is the way.) So, why not play Jadzi, Oracle of Arcavios
as commander? Good question. Not too sure, actually. The deck should look roughly the same, I recon, but Gretchen and Biomancer would be cut. Don't expect to put up a better fight than decks who play the Cultivator Colossus combo lines, but have excess to black tutors.
Secondly, some ideas on power and improvement. I recon that this deck would benefit from cards like Eldritch Evolution and Neoform, if you care to throw all 1 mana value mana-dorks into the mix. Dorks will very likely increase the consistency of this deck, as it enables Gretchen Titchwillow to activate more quickly and more often. We then would remove the beefy stompers, going even more all-in on the lands-to-creates route. The reason I'm hesitant to do so, is that I've got a Kinnan, Bonder Prodigy deck lined up as well, and I'd like those two Simic decks, which both have beats as wincon, to be significantly different. As it stands, though, I foresee this deck being sllooowwww. Edit: After testing a bit, at turn 8 you can expect to have a lot of lands in play.
Lastly, all considerations above are just the basic idea for this deck/commander. I will be playtesting/goldfishing more when I get around to it, and will be making changes, most likely. Feel free to add, cut, change or copy.
Second edit: I've upgraded the whole deck to be a whole lot faster and more competative. Goldfishing now with more fast mana, tutors and more efficient counterspells.
Third edit: Scaled it down (to closer to what I onw in paper) and made some adjustments according to some pEDH stuff I've seen around. Most notably: Gush and Mystic Sanctuary. I also had a Stone-Seeder Hierophant laying around, so I decided to put in there. I think it's a fun deck to play if you don't mind being low on creatures. Some creatures are added to the Maybe section, which are creatures whose power/toughness are based on lands or forests you control.
