As hinted at the title of the deck list, this deck aims to play more of a survival game - not so much by controlling other players' boards, but rather by making yourself difficult to hit in the early turns, or simply by weathering them out and recovering lost life with Trostani. Eventually, the board position that you've been incrementally building up arrives at an explosive point where you can simply start killing people. Even if reset, you will have built such a large advantage of land count and utility, that you can repeatedly explode from recovery into recovery as needed.
Populating Value Targets
Before jumping into the nitty gritty of the deck, one thing to touch on quickly is how the cards Mirrorpool, Séance, Mimic Vat, and Blade of Selves serve to make token copies of creatures. This allows for Trostani to populate them and keep them around permanently, which adds a large amount of value and strength to her ability. This is important to consider while piloting the deck and judging the value of situations that may arise.
For example, in one case several opponents jumped through several hoops to finally kill my Vitu-Ghazi Guildmage, only to have it placed on a mimic vat, so that I was able to create a token copy of him, and then use that token's own ability to populate himself before my next turn even came around, leaving me with a copy of my guildmage in play, as well as a copy safely on the Mimic Vat for future need, in case the token were removed again.
How to Play
This deck aims to balance developing the board state with self protection. The early game is dedicated to setting up your land searching and ramping capabilities, followed by the card draw options. When exactly you drop Trostani depends on your ability to make tokens, as well as how much fire you're taking and how much you need to prioritize lifegain. If there aren't any majorly advantageous plays available, it is often correct to simply run out Trostani early. Since we don't have any haste enablers, you'll want her out a turn before your token engines anyways, and the incidental lifegain will always help buffer. She's also a fairly solid blocker on her own.
Knight of the Reliquary is perfectly fine to run out early as well. While he's one of our ways to dig up our Glacial Chasm, he can be used to ramp early on by fetching lands like Myriad Landscape and Krosan Verge. At worst, he can also replace a tapped land with an untapped one, giving a slight mana boost if needed on crucial turns. Finally, if you have the luck to pair him with Rings of Brighthearth, he does turn into straight-up ramp, and his ability to bring out fetch-lands becomes exceptionally powerful. Be sure to consider fetching up a Mistveil Plains with his ability, so that you can cycle lands back to the bottom of the library for reuse.
The next aim of the deck is to focus on protection. Since Trostani requires a turn to become usable, it may take a few turns of populating tokens to arrive at a sizable enough army. Trostani is quite simply not the fastest racehorse on the track. She can take a bit of time, and your strategy and progress is very visible during all of it, which makes it easy to prioritize you as a threat. Having lots of mana can help reduce that time required, which is one reason I focus so heavily on ramping during the first phase of the game. This protection phase of our strategy is where we really embrace the fog effects. Due to our life total buffering and high density of fogs, this Trostani deck is not terribly worried about creature-based strategies. Save your removal for combo interactions, cards that are disrupting your ramp or draw, or other non-damage win conditions, unless absolutely necessary. Let the Constant Mists, Knight-Captain of Eos, Invulnerability, and Glacial Chasm handle the direct damage options. You can populate the soldier tokens for Kinght-Captain of Eos, and if the Knight dies, you can mimic vat and then copy [i]him[/i] as well. On the other side, both Glacial Chasm and Invulnerability also stop non-combat damage, so they can both be used to stop Fireballs or other direct damage sources, such as Warstorm Surge triggers. You can even pull Glacial Chasm out at instant speed with Knight of the Reliquary, Budoka Gardener, or Crop Rotation.
Once you have your board situation under control, the next step is to find a big token, populate it a lot, and then kill people with it. From Titania, Protector of Argoth to Herald of the host, to repeatedly recycling the token producing lands, the deck has numerous top-end threats - many of which are strong enough on their own to close out the game, even if you can't populate them.
Keeping Glacial Chasm Around, and Responding to Graveyard Hate
Glacial Chasm can hurt, and often times it can hurt you a lot. On top of that, each time you play it is a tempo loss. These qualities are offset in value by how much damage and life it will save you in the long run, but knowing when to let go of the Chasm versus when to keep it around is important. Thankfully, due to having Trostani as a Commander, we can easily offset the life payments for Chasm for quite a long time. This means that it's perfectly ok to let the Chasm stick around longer in this deck than some other decks would. When it comes time to let go of the Chasm, either to attack or to reset the life payments, you have a number of recovery options available to you in order to replay it after combat and keep your protection (or even during combat with Sun Titan). Crucible of Worlds, Life from the Loam, and Tilling Treefolk are the obvious ones, but you can also utilize Mistveil Plains to put it back into your library to bring it back out with Knight of the Reliquary. Putting a Tilling Treefolk or Titania, Protector of Argoth on the Mimic Vat (or populating a Séance token of them) is another great way to get it back at instant speed - perhaps in response to graveyard hate (Glacial Chasm [i]will[/i] get targeted). If you do fear a response of graveyard hate, pay attention to available mana for it, and try to keep your Mistveil Plains open to respond, or possibly one of the populate tricks mentioned above. At times though, it's ok to let the Chasm go if you're ready to take the aggessive stance.
Other options for getting the Chasm out in a hurry would be to run Walking Atlas, Budoka Gardener, or Sakura-Tribe Scout, as it can be quite a problem to have the chasm stuck in hand on an opposing turn.
Dealing With a Wrath Heavy Meta
Since this deck aims to build a large board presence over several turns, it can run into delays when opponents use wrath effects wisely. While the density of enchantments in the deck can mitigate traditional wraths somewhat, if you frequently run into Austere Commands or Akroma's Vengeance, you may need more protection and recovery options than are currently in the deck. Consider Rootborn Defenses as a possible inclusion, as well as Dauntless Escort, and possibly even Spirit Bonds. This will allow you to keep Trostani and your army through the wraths, that way you maintain at least some of your board presence.
Against more standard Wrath of God effects, Mimic Vat and Séance can help recover your boardstate very quickly, by populating back in the better engines that you have.