The marquee additions in Baldur's Gate 3 Patch 8 are probably , the subclass, and the cantrip, but there's also a new sicko combo that's taken the BG3 Builds subreddit by storm: plus .
Neither of these are fully new, but Patch 8 did a complete revamp on Shadow Blade, transforming it from an interesting novelty into a spell you can hang a full build on. Resonance Stone is unchanged, but this longtime powergamer's delight has found its perfect partner in the new Shadow Blade, and I think I've finally settled on my Patch 8 Honour Mode character because of it.
Resonance Stone is the Jock Rock, the Rock that Makes You Stupid. It's some kind of Mind Flayer tchotchke you can find in Act 2's Illithid Colony, in the room with all the zombies and the brain-reading head machine (if you know, you know).
The Resonance Stone projects an AOE field that gives everyone in it (friend or foe) the "Steeped in Bliss" debuff: Disadvantage on mental saving throws (Wisdom, Intelligence, Charisma), advantage on physical checks, and, crucially, vulnerability to psychic damage—all psychic damage inflicted on anyone in the bubble is doubled.
Until now, consistent sources of psychic damage to take advantage of this were relatively rare: , certain , and the , to name a few. The Shadow Blade spell was always interesting: Summon an equipable shortsword that does 2d8 psychic damage (plus your melee ability modifier), but it could only be cast via a , and it required concentration, meaning you could lose it on getting damaged or stunned.
But now Shadow Blade is a different beast: Sorcerers, Warlocks, and Wizards can not only learn it as a normal level two spell, they can upcast it with higher level spell slots to improve its damage. That none-too-shabby 2d8 Psychic damage gets boosted to [[link]] 3d8 or 4d8 with level three and five spell slots respectively. It also, crucially, no longer requires concentration—once you've summoned the Shadow Blade, it [[link]] just sticks around until a long rest.
Basically, we're in spellsword heaven. Shadow Blade starts out incredibly strong even at level three—when you first get second level spells—outclassing nearly every other weapon in Act 1, and it only gets better. Pair it with the Resonance Stone, and you're looking at a minimum of 8-64 damage on every attack with the max-upcasted version of Shadow Blade.
There are all kinds of other synergies to take advantage of as well: The Shadow Blade being a short sword means you can put a useful stat stick like the in your offhand, and the large dumber of dice at play means that critical hits, as well as the feat, become especially powerful. Of course, you can still to your heart's content with this summoned sword.
Also, it just has to be said: The summoned mind-sword is just extremely cool conceptually. There is one achilles heel here, though: Psychic damage-immune enemies, most notably and the , but with foreknowledge you [[link]] can plan around these particular fights.
The new Bladesinger is primed to take advantage of this one, as could some manner of Sorcerer-Paladin multiclass, but I'm feeling Hexblade: I'll be opting for a Hexblade 9 / Champion Fighter 3 build for maximum crit hit action. However you choose to take advantage, it's seriously boom(ing blade) times for spellswords in BG3.