Curse of the Allflame: Content Livestream Summary
Overview
Curse of the Allflame League Mechanic
In the Curse of the Allflame league you'll encounter a new NPC, Valerie, who you'll join on a journey to the depths of the ocean in search of valuable treasure! Valerie is a corsair and captain of The Sovereign, a vessel powered by mysterious energies.

The Captain of The Sovereign
During your journey across Wraeclast, you'll find Charts which are very similar to maps, only they're instead used specifically to explore the ocean. Using a Chart will allow you to access an area in the depths of the ocean affected by the modifiers of the Chart, which typically make it more difficult and rewarding.
A bathysphere will enable you to make your way from The Sovereign deck all the way to the dark depths of the sea. Once there, use lanterns powered by the Allflame to enable you to explore the ocean floor, providing a large area to traverse without the risk of drowning. Beware though, you only have a limited number of lanterns to place and each lantern will have a limited duration - once time runs out you'll need to return to the bathysphere to avoid drowning.

The green indicated Lantern safe areas
Charting enough areas will allow you to connect them together to create a Voyage - a much bigger excursion into the deep. Voyages allow you to claim the rewards of Charts again, but this time they'll be amplified by various modifiers such as those on the edges of the Voyage plan map, impacting adjacent areas with lucrative boosts.

Plan your Voyage
On your journey you'll also encounter a valuable new resource - Dead Man's Sulphur. This resource fuels a powerful new crafting mechanic known as Allflame crafting. Use the power of the Allflame to see ghostly outcomes of specific crafting mechanics on your item, allowing you to pick one.

Make your choice
Mercenaries of Trarthus goes Core
The league mechanic from patch 3.26, the Mercenaries of Trarthus, is returning to Path of Exile in a reworked, core version in Curse of the Allflame.
You'll encounter Trarthan Mercenaries in areas beginning in Act 3 who will challenge you to a duel to the death. You can select an item from their inventory as a prize prior to the duel, to claim for your own should you win. However, in addition to your selected reward, the mercenary will also join you as an ally for a number of areas thereafter. Note that unlike in patch 3.26, you will not be able to customise the equipment of your hired mercenary.

Put your money where your mouth is!
If you don't want any of the item that the mercenary has to offer, you can instead choose to itemise their presence, allowing you to spawn them in a future area with a new set of items. This itemised mercenary can also be traded to other players.
Like any league that goes core, the Mercenaries of Trarthus also has its own set of passives added to the Atlas Tree that you can specialise into should you want to farm this content in endgame.
New Scion Ascendancy: Luminary
Finally the Scion has three ascendancy options, with the new Luminary ascendancy in 3.29! This ascendancy pairs with the core introduction of the Mercenaries of Trarthus because it's all about specialising into mercenaries!

The Luminary Ascendancy
Unlike any other class, the Luminary will be able to keep a mercenary permanently, joining them in every area they venture to. The Luminary will also be able to customise the equipment of their hired mercenary like the original version of Mercenaries of Trarthus from patch 3.26. This means that you can curate a build with a powerful supporting mercenary, or perhaps instead you'll play a supporting character and allow your mercenary to be the damage dealer - the choice is yours!
Abyss Reworked
The Abyss mechanic in Path of Exile 1 is receiving the Path of Exile 2 treatment, with updated gameplay systems. The old version of Abyss in maps is going away and a more modern version will now replace it. That means no more backtracking to chase Abysses.
Slaying monsters on top of Abyssal cracks in areas will cause the Lightless to flood out of the dark depths. This new version is more visceral, and the Abyssal monsters have also received significant upgrades, with scarier abilities and mechanics.

Close the Abyssal cracks!
Scarabs and the Atlas Tree has also been updated as part of this change, and there's also a new Abyss Pinnacle Boss to hunt down in the endgame!
Legion Rewards Updated
The Legion league mechanic has received a powerful new exclusive reward to set it apart from other mechanics, which entirely replaces the old incubator system.
You'll be able to use new currency items, Enshrouding Crystals, on Unique items. This will allow a Unique item to be placed in a special charging crystal within the Domain of Timeless Conflict. Upon charging the item, it can be shattered to reveal a Vestigial Unique of the same item type, which retains a special modifier from the previously Enshrouded item as an implicit.

Vestigial Unique Gloves born from Enshrouded Shaper's Touch
There are also some other improvements to Legion, such as the removal of Unrelenting Emblems and subsequent improvements to the base version of the Domain of Timeless Conflict, including higher difficulty and more rewards, and a change visually to rewards in this area which is now displayed as charged crystals rather than symbols on screen.
Atlas Anomalies
In patch 3.29, completing maps that are affected by a Voidstone will have a small chance to reveal an anomaly on the Atlas map. Anomalies can be run a single time, and are somewhat similar to Unique map areas or special areas found in other areas of the game.
For example you may encounter Cadiro Perandus who will offer you a selection of Unique items that can be pruchased for gold. You may also find an anomaly that's a fully revealed Heist Blueprint, allowing you to interact with this mechanic without actually investing into it. Note that some endgame rewards, such as the Nameless Seer, can now be encountered in an anomaly area rather than at the end of a normal map.

Cadiro encountered in an Atlas Anomaly area
Socket Colour Changes
Socket colours on items no longer prevent any type of Gem from being socketed within - you can now socket any Gem into any socket regardless of the socket colour. However that doesn't mean Chromatic Orbs are going away, because socket colours will now be important for another new feature.

A blue Gem socketed into a red socket
Items will now typically be found with white sockets, but you can use Chromatic Orbs to reroll the socket colours, guaranteeing at least one coloured socket. Upon placing a Gem into a socket of its colour, such as a Strength or Red Gem going into a Red Socket, you'll gain a bonus 10% to the Quality of that Gem.
Self Cast Spells Buffed
There are a large amount of new additions and balance changes in Curse of the Allflame to improve self-casted Spells. The Assassin, Occultist and Inquisitor are all receiving new Notables to improve self-casting builds on these classes. Additionally, aside from a huge balance pass across Spell Skills, there are some new Skills to enable Spells in new ways, such as Pact of Ghorr which empowers Damage Over Time Spells.

Spirit Infusion buff from a new Occultist Notable
New Supporter Packs
There's a new set of supporter packs available as part of the Path of Exile: Curse of the Allflame launch to aid the future development of Path of Exile and Path of Exile 2. You can find more information about these new MTX packs here.

The Plague and Remidus Packs