Yorick, Karma and Yunara can all be kept in the final board for synergies, which makes Blossom very intuitive to play. You only need to use the Remover to transfer items in such order below.
Yorick → Sett
Karma → Ahri
Yunara → Ashe
Unlike previous sets, Ashe is not a marksman anymore, she is now a caster.
So remember not to build Guinsoo and Kraken on her. This is a common mistake found on a lot of players.
Instead, please use those Recurve Bows to build Red Buff.
Her ultimate basically hits the whole board, that's why she is best at applying Burn/Wound with Red Buff. (Karma can also carry Red Buff early if your Yunara is not upgraded.)
Both of your carries, Ashe and Ahri are Casters, so extra Tear of Goddess are actually really good. Spear of Shojinand Blue Buffare about the same on them, just Spear of Shojin is slightly better on Ashe. Blue Buff is slightly better on Ahri.
This is one of the strongest board during Stage 4.
For your Primal Spirit, always choose "Blessing of the Bear".
This is because, in Blossom, a very common situation is that Ahri casts her ult and deals a huge amount of damage, but can't finish off all the enemies. Blessing of the Bear allows you to execute low-health enemies, which will solve the situation perfectly.
Positioning tips:
Sett with Gargoyle Stoneplate solo-front is the best.
Everyone stands back so Sett can make most value of the Gargoyle Stoneplate.
Rolling Strategies:
Roll mainly at Level 8 and 4-2. Don't roll straight to 0, keep at least 10 gold unless you have to.
If you are close to your 2★ 4-costs (Sett, Ahri, Amumu) and are holding pairs --- try to 2★ them before going Level 9. This will secure a Top 4! And, you could also get 5-costs such as Ashe, Gnar, and Kennen if you are lucky.
How to Choose Between 5 or 7 Blossom in the Mid Game
7 Blossomgives 4 extra goldper round, but not actually a lot of upgrades to stats. Once you have enough econ in the late game, go back to5 Blossom and tag in 5-costs!
However, 4 gold per round is a lot of gold during mid-game, so if you can get 7 Blossom as soon as possible, it's almost always worth it! (especially during Stage 3 and Stage 4)
Importance of Blossom Emblem:
With a Blossom Emblem (Spatula + Rod), we can go 7 Blossom easily at Level 8 without having to find Ashe.
7 Blossom will give you a lot of gold, making it easier to go 9.
The Spatula can come from many sources, such as U.R.F., Urf's Gambit, Carousel rounds, PvE drops, etc.
If you can rush 7 Blossom either by having an Emblem or finding an early Ashe, you should definitely do that.
Flexibility:
Between Sett and Amumu, whoever gets 2★ first should hold 3 items. Malphite is also very playable if he is 2 starred.
If we find 2★ Sivir first, she can also hold Ashe items, since she is also an AD Caster.
If we find 2★ Zyra first instead of Ahri, you can instantly play her as well, because Zyra activates 2 Summoner with Yorick. (Same with Soraka, but Soraka is 2 Executioner with Yunara.)
You don't really need a 5-cost tank in this comp. Sett is just as strong as a 5-cost tank when you have 5 Blossom activated. Amumu is also a great tank if you have extra tank items!
But don't switch out Vi for Amumu if he is not 2-starred. This is because Primal is very strong in mid game.
5-cost Fighters such as Gnar and Kennen are amazing on top of everything you have! Especially when they are 2★, they are so strong that they can literally win you the game!
Gnar and Kennen are both great with Thief's Gloves (TG), which makes it easy to itemize them on top of your duo carries.
If you can find 2★ Lux, transfer items from Ahri to 2★ Lux. It doesn't matter what synergy Lux has; 2★ Lux is still the strongest AP carry in the game.
Blossom Lux makes it possible to go 9 Blossom, which will allow you to buy 2 wisps per round, and buying them will give you 4*2 = 8 gold. Plus the combat advantage from wisps, it brings a huge advantage in general.
If Blossom is uncontested, you can also try to 3★ Ahri and Sett at Level 8 with augments such as "One Buff, Two Buff," and "Commerce Core." This strategy works really well, especially when you have a Champion Duplicator and are ahead of the lobby.
A 3★ 4-cost champion will be able to beat 95 boards with ease, making it the safest way to secure a first. But be sure to scout the lobby, since each 4-cost only has 10 copies in the pool. Once 2 copies are out of the pool, it becomes almost impossible to 3★ them. Unless you have two Champion Duplicators, in which case, in my experience, almost no one can stop you.
The best timing to roll for a 3★ 4-cost is when almost no one has been eliminated, but the remaining players also have very little HP.
This is because most of the 4-costs have already been taken out of the pool. If players are eliminated, however, those champions will return to the pool, making it harder for you to find Sett and Ahri.
5 Blossom allow wisps to appear in your every shop, which is crucial for you to 3-star 4-costs later on. Certain Wisp such as "Blood Ritual" (only appear during Stage 4) which offer a champion duplicator is extremely useful.
Wisp - "Barter" allows you to sell a champion for 250% of its value, you can use it to generate more gold during the rolldown by selling a 2-star 4-cost which will earn you 24 gold.
Alternative Path
If you didn't hit Sett or Ahri during Level 8, also don't worry, check out this AP Flex 84 guide, you still have an option regardless. <3