I would say that you would be safe dropping 3-4 lands with your current amount of ramp.

I would suggest adding Sage of Hours for the extra turn loop (just be sure to take the turns quickly if opponents don't scoop to it). I would also add Shrieking Drake so that you can turn excess blue mana into experience counters. I am primarily a combo player and totally understand if either of these are play patterns that you don't like. Just throwing ideas out there.

On an interesting side note: Though the choices made from previous "draws" do not limit what choice you can make for future ones, what card was exiled might. You get to look at each card as it is exiled and before you have to make a choice on where the next card is exiled from.

Replacement effects are not triggers and do not use the stack. They simply replace one event with another. When Windfall resolves the active player will "draw a card" however many times in a row. Each is a different game event that will be replaced with exile the top card of an opponent's library, the choices made for each can be the same or different. Then the process will be repeated for the next player in turn order until all players have "drawn".

121.2. Cards may only be drawn one at a time. If a player is instructed to draw multiple cards, that player performs that many individual card draws.

121.2c If more than one player is instructed to draw cards, the active player performs all of their draws first, then each other player in turn order does the same.

And I like how you read the title and literally none of the post and decide to make a comment on it. The two sentences not in spoiler blocks explain that it was an idea for a hub, but because of the support it received it is now a selectable format to tag your deck with. Grats on getting uppity about an announcement of updated deck builder features on this deck building website though

Doubling Season itself never creates a token or adds counters. It causes other effects to create double tokens and add double counters.

"If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead."

Tombstone Stairwell's destroy clause applies to all tokens created with it. Even though created with it because of doubling season.

It seems like with the whole Sundial of the Infinite thing people may be focussing on the wrong thing about the end step trigger to me. Sundial will allow everyone to keep their tokens. Tombstone Stairwell says to destroy the tokens, not sacrifice them. If you can grant your board indestructible you can keep all of your tokens while everyone else's gets destroyed.

The best colors for these shenanigans seem to be Abzan with Ashaya, Soul of the Wild and Terra Eternal or Timber Protector; Tribal indestructible cards and Conspiracy; and Avacyn, Angel of Hope. Mycosynth Lattice and Darksteel Forge are a colorless way to do it. This isn't an exhaustive list, but merely a place to begin if you like the line.

If the boardstate is EXACTLY as you described, your opponent will have a 4/4 frog and it's controller's life total will be doubled when it deals combat damage to a player.

The reason for this is that an object's characteristics are applied in a series of layers and then within those layers in timestamp order. Since you played the Frogify after the Hivestone the creature gains the creature type sliver and then loses all creature types besides "frog". Cloudshredder Sliver will not apply since it isn't a sliver. The Celestial Mantle will actually have all of its effects no matter the timestamp because Frogify sets the base P/T and Mantle gives a buff instead of modifying base; and the life doubling ability is not granted to the creature.

Shoot, I just noticed that I forgot Pathways. Honestly once you get below Shocks it is mostly down to personal preference as to the exact order of land cycles. I know that many people wouldn't put filters as high as I have them, but I am greedy with mana pip density and the possibility of a turn 2 Necropotence off of Forest, Birds of Paradise, Twilight Mire makes my little combo player heart all a flutter.

The slow lands are unplayable in Modern and Legacy, the only other format that I play enough to have thoughts on is EDH and oh boy do I have some thoughts. The TL;DR is that I agree with Gleeock's assessment on power.

Lets preface this by saying that I play on the higher end of casual. I am primarily a combo player and enjoy doing "unfair" stuff in a game, but by no means am I kidding myself that I am playing cEDH. Slow lands are also unplayable in cEDH and I know this.

In a 6-10 turn sub-hour long game of EDH slowlands are perfectly playable. They become even more playable the slower your meta is. Any keepable hand is going to guarantee that they come in untapped if you draw them, if one is in the opener it isn't a huge deal to play it tapped turn 1.

My positive opinion of slow lands may also come from the fact that when it comes to deck building I am more of a tuner than a brewer. So, card assessment happens in context of a deck, not in a complete vacuum. My typical deck is 2 or 3 colors. It contains enough lands with basic types that I don't need more fetch/Nature's Lore/Farseek targets for fixing, but few enough that any two lands is a much smaller ask than a land with one of two specific basic types. Basic count is low enough that tangos aren't ideal. Any of the "guildgate with a minor upside" have the downside of ALWAYS coming in tapped and so are going to be placed lower than slow lands.

If pressed (and I am pressing myself because you asked people's opinions on how good slow lands are) in my decks in my EDH meta I would put my top 10 2 color land cycles as:

1. Fetches

2. ABUR Duals (Never personally going to have any)

3. Shocks

4. Battlebond Lands

5. Filters

6. Pain Lands

7. Horizon Lands

8. Slow Lands

9. Check Lands

10. Fast Lands

Honorable mention of Tango Lands in case someone has a problem with fetches on my list of 2 color land cycles.

"Our boy" Jace is a Marty Stu and I don't know who left fanfic writers in charge of Magic lore.

Each time a player would receive priority all triggered abilities that have triggered since the last time a player received priority will be put on the stack in APNAP (active player, non-active player) order and if a player controls multiple triggers being put on the stack at the same time that player gets to choose the order. All attack triggers and exert triggers happen during the turn based action of declaring attackers, so they will all be put on the stack at the same time. There is no differentiation made.

The middle bit of your explanation of priority in the declare attackers step is a bit unnecessary since the process of a player receiving priority involves putting triggered abilities on the stack. If it helps you to keep it straight though, there is no harm in separating checking SBAs, putting triggers on the stack, and a player receiving priority into distinct things as long as you realize that they happen in that order and any time an SBA is performed or a trigger is put on the stack you will start the sequence over by checking SBAs again.