I'll put this mostly into comments instead of it being a wall of text. I've scavenged these from a bunch of different articles and videos, plus some help from Kolanaki. Some of it is on the wikis now
Other new weapons
Three new weapons from the categories that Shadow of the Erdtree added are now available in the base game world.
Reverse-bladed sword: Curved blade wielded with a backhand grip, said to have originated from the hidden realm of shadow. The style of combat associated with this weapon is marked by spinning slashes and gouging thrust attacks.
Reed great katana Large katana with a long, heavy blade. A weapon unique to warriors of the Land of Reeds. Designed for aggression, this armament requires the wielder to throw their entire body into swinging it. The slashing attacks of its honed edge incite blood loss.
Ritual thrusting shield: A "thrusting shield," or combined weapon and shield. Enables the wielder to attack and guard simultaneously. An armament once used in rites of combat performed to honor the Erdtree, now lost to time.
Nothing too surprising here, with one exception: the reverse-bladed sword's description suggests that the Realm of Shadow is not as much of a secret as Marika might have liked. If the sword is "said to have originated from the hidden realm of shadow", people have to know about the RoS to be spreading rumours about it