Constantine heads into the asylum looking for his patient and later the Legends arrive with Waverider in episode 3x10 "Daddy Darhkest".
The young Damien Darhk assassinates Dr. Vogal and then Nora and Ray show up to save him in episode 3x13 "No Country for Old Dads".
From episode 1x03 "Rogue Wall Enthusiasts". A new soul is transferred into Agent Weedle's body in episode 1x04 "Watkin". The two detectives find a pile of bodies in the building in episode 1x05 "Very Erectus". Appears in 3 more episodes.
Col. Riggins and Sgt. Friedkin put on their gear while preparing to talk to the Rowdy Three in episode 1x05 "Very Erectus".
Webb holds his daughter for the first in episode 1x07 "Weaponized Soul".