Generally speaking, it depends on how heavily the blue deck in question leans on Jace or whether they have a combo element. RIP Miracles is the deck that sends me slamming Slaughter Games the hardest. They have a combo element that needs attacked (Rip/helm) and Jace is their primary backup wincon, with their secondary backup (Entreat) being easily solved by just sitting a Deed on the table).
BUGStill has two lines of winning: Jace ult protected by oodles of removal/counter, or Manlands.beatdown. If you strip out their Jaces, they are FORCED to attack you with manlands to win, which means you can junk up their engine by Deeding@0, playing Huntmasters/Thragtusks/Avenger, Ruination or Sowing Salt in particular, and so on. Also, Jace is a 4-of blue card, which makes their Forces worse.
Esperblade I don't usually bring in the Slaugter Games vs. They just don't lean on Jace hard enough -- he usually sits there brainstorming every turn, and while he's annoying, he's usually like a 2-of. It's just not worth boarding anything out for them.
Generally, if Jace is a 3- or a 4-of, then bring Slaughter Games in specifically for Jace.
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Alternatively, combo decks.
Taking TES's Burning Wishes, Sneak's Emrakuls, OmniTell's Omnisciences, Belcher's Belchers, High Tide's Time Spirals, RIP's/enchantress's Helms, Dredge's Dread Returns, and so on is all big game. So you board them in there.
12post is a unique scenario. I'm increasingly becoming convinced that it's correct to take their Crop Rotations, because we can ramp to 7-9 faster than they can -- they can just go further than we can, into the 15-25 range. If they don't have Crop Rotation -> Glacial Chasm, we should easily be able to kill them before they drop space monsters.
12post is also the ONLY deck where I board in all 3 Slaughter Games. This is because there is never a situation where you want to Burning Wish for Slaughter Games over Ruination. Otherwise, I'm of the opinion that it's always correct to leave one Games in the board to Wish for and increase your effective copies of.
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The Red Blasts depend on how blue the deck is. Something like BUGStill sees all 3 windmill slammed. Esperblade....isn't a very blue deck. I usually only board in a pair of them there.
So like, consider Esperblade as an example.
Let's say the opponent is on a very stock Esperblade list...nothing that seems unusual to me. My "standard" plan pre-tweaking would be to go
+2 Red Elemental Blast
-1 Green Sun's Zenith
-1 Veteran Explorer
The rationale is that Esperblade is a heavy attrition deck. Being able to turn your Burning Wishes into a Green Sun's Zenith is a powerful thing in this matchup. You also don't have a large number of relevant wish targets vs Esperblade, so you want to increase the number of things you actually want to wish for. Trimming out one Veteran makes sense because they can accelerate to the same degree that we can, and while we use it better, we want to keep them on 2-3 lands as opposed to 4-5. 4-5 means that they can use Snapcaster better, they can hardcast Force (very relevant since they aren't a very blue deck), they can play+flashback Lingering Souls, they can drop jace, they can drop Elspeth, and/or they can Clique+Karakas lock. Therefore, Esperblade is a good deck to use Veterans as deterrents to attack / Swords bait, but lean on Sakura-Tribes and Wood Elves as your actual ramp.
Miracles, then. Again, assume perfect stock list and opponent, no tweaking.
+3 Red Elemental Blast
+3 Slaughter Games
+1 Scapeshift
+1 Maelstrom Pulse
-4 Burning Wish
-3 Veteran Explorer
-1 Cabal Therapy
Explorer is obvious here. Miracles is one of the few decks that has as many basics as we do, and ramping them is usually a death sentence. They're glacially slow, so we can afford to lean on Sakura-Tribes and Wood Elves.
Most Miracles lists rely fairly heavily on their CounterTop engine to protect themselves. Red Blast is good to stop Counterbalance from landing if possible. Slaughter Games goes after Jace and Helm. The Scapeshift and Pulse come in because they're useful to have, and we're boarding the Wishes out. You board the Wishes out here because of the danger of Counterbalance. If they assemble CounterTop, then Burning Wish becomes real bad. It's much harder for them to counter Scapeshift or Pulse than it is Burning Wish, even if we'll see them with less frequency.
It MAY be correct to just give up on the Counterbalance fight and leave the REBs in the board in lieu of more fringe wish targets, but I like forcing them to deal with the threat of REB. Sometimes REB will win the Counterbalance war. Sometimes they'll have to draw off of Top to counter the REB, which will leave them vulnerable to a higher-drop threat. Sometimes you can Deed away the Counterbalance and the REBs are live again. It varies.
Now, here's one of those tweaking things we were talking about. Sometimes they only run 1 or 2 Counterbalances main. If you suspect that your opponent isn't running Counterbalance or isn't heavily committing to it, you can leave the Wishes in and the Wish targets in the sideboard. In that event, you would just go:
+3 Red Elemental Blast
+2 Slaughter Games
-3 Veteran Explorer
-1 Cabal Therapy
-1 Burning Wish
I still like shaving a Wish here. The danger of Blue Blast out of Miracles is VERY high -- they typically pack it for other problems that they face, but they'll bring it in vs us.
Here's a sample BUGStill list that got posted today in Caleb's article on CFB. I personally don't like it, but it's a good starting point because the nameless durdle masses will see it in a CFB article and build it, whether it's good or not.
Main Deck
2 Misty Rainforest
4 Polluted Delta
2 Verdant Catacombs
3 Underground Sea
2 Tropical Island
2 Bayou
2 Creeping Tar Pit
2 Wasteland
2 Mishra’s Factory
1 Swamp
1 Island
3 Jace, the Mindsculptor
2 Liliana of the Veil
4 Deathrite Shaman
3 Tarmogoyf
3 Snapcaster Mage
3 Standstill
1 Life from the Loam
4 Brainstorm
4 Force of Will
2 Counterspell
2 Spell Pierce
2 Disfigure
1 Dismember
3 Abrupt Decay
Sideboard
2 Nihil Spellbomb
1 Duress
2 Flusterstorm
2 Thoughtseize
3 Vendillion Clique
1 Maelstrom Pulse
1 Tarmogoyf
3 Engineered Plague
This deck has NOTHING against Burning Wish, unlike mine which has 3 Snare + 2 BEB + 2 Snap. Vs this deck you wouldn't board out the Burning Wishes, at all. Instead, you would likely do something like:
+3 REB
+2 Slaughter Games
-1 Pernicious Deed
-2 Huntmaster of the Fells
-1 Thragtusk
-1 Green Sun's Zenith
This list is weird, since you'll likely see Tarmogoyf main. Goyfs and Deathrites will encourage you to keep in more Deeds than you usually would, as well as having to keep in more Thragtusks and at least one Huntmasters. This seems like a weird thing to want to take out, since Huntmaster and Thragtusk both require BUGStill to invest more resources in dealing with them, but in my experience, they're the better Deed deck. We don't need their lifegain here. Our plan vs BUGStill is to go to the big-game with Primeval, Avenger, and Scapeshift combo-kill. Going aggro against BUGStill won't work very well. Huntmaster in particular is usually ass here, because they have Disfigure, Abrupt Decay (for when he flips), and Mishra's Factory -- alongside Goyf, who will be bigger than he will, Snapcaster, who can flash-trade, and Pernicious Deed for the sweep. You can't bog down fighting them at their own game.
Boarding out the Green Sun increases our accessibility to it, which is important to establish Avenger or Primeval.
The Wish decision tree for BUGStill looks something like this:
If no nat.draw Slaughter Games, Wish for Slaughter Games, take Jace.
If nat.draw Slaughter Games, then Wish for the situation:
If land-light, Wish for Ramp
If opponent has been Therapied and you have lethal lands, Wish for Scapeshift
Else Wish for Green Sun (pref. for Primeval or Avenger; also for E.Wit to regrow Scapeshift)
The last option is usually only after your sideboarded Scapeshift has been countered or if you have some reason to not Scapeshift (they have an onboard Wasteland and you're at 7 lands, for example).
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tl;dr -- always have a plan with your wishes in your board. Don't board out Green Sun just for the sake of boarding it out. I only board it out in really heavy attrition matchups where you need that extra threat, AND where you think you'll be able to resolve Burning Wish, AND where you don't have 3 or 4 options that are better. Like, consider Jund. Jund is the type of deck where you might want to board out a Green Sun. But vs Jund, you'll ALWAYS wish for something else. You'll Ruinate their mana base, or you'll just win, or you'll want to Pyroclasm their board, or so on. BUGStill is very close to this threshold, but it's a bit different because you need to worry about your Wished Scapeshift getting countered, so you want something else that you can Wish for when you go big.
See what I mean? It's a weird subject. Unfortunately, I can't just download my knowledge about how the play the deck into everyone's heads, lol.