After casting Soul-Infused Sword, he attacks the target 6 times in quick succession rather than dealing damage instantly.
(Active 3) Soul-Shadow
The Clone mimicks his 1st and 2nd active ability. It won't attack if Greysoul gets CCed. The clone will gain Soul Plunder as well. It will not grow in size or become red when Magnify is used.
(Passive 1) Soul Plunder
One can confirm the activation of Greysoul's Soul Plunder by the critical buff icon in his buff-bar.
(Passive 2) Soul Focus
Greysoul and Gaela have some sort of relation. They were once archenemies. Nothing more is currently known.
It's not wrong to assume that Greysoul and Blackaria are in a romantic relationship. The characters of the story also know that, and point it out indirectly.
Greysoul was disabled during or after sealing Ragnorak. In Dark Legion's Quarters Stage 9, it is revealed that Greysoul waited inside of Ragnarok to keep the seal intact. He then frees himself after Ragnarok broke free.
Greysoul's active abilities resetwas added in Chapter 3.
Greysoul uses only his Long Sword for Auto Attacks. Soul Shadow's Clone will only choose close combat for Auto Attacks.