Zaris' spell blinds all but the swarm of bats engaged with Corban, whose blade, at that same moment, cut the last strand of life from the giant bat. The bats, however, seem unaffected by the blindness.
Kaiakas turns his attention to the sad and manages to kill a few bats, but they are still very numerous.
Reina hefts her battle axe and swings again, following Kaiakas' lead and turning her attention to the swarm.
The swarm around Reina and Kaiakas converges on Kaiakas, but the bats are less focussed than before and he is able to protect himself from th force of their bites.
The other swarm goes after Corban, overwhelming him. As he falls the swarm flies towards the tunnel you came a through, past Zaris and towards the stairs. The last giant bat swoops in at Reina but she deftly avoids the attack.
Giant Bat 1 and Bat Swarm 1 are blind (but it has no effect, as bats have blindsight)
Corban hits and defeats Giant Bat 2
Kaiakas hits and deals 3 damage to Bat Swarm 1
Reina hits and deals 5 damage to Bat Swarm 1
Bat Swarm 2 hits Corban for 9 damage
Giant Bat 1 misses Reina
Reina and Kaiakas are engaged with Giant Bat 2 and Bat Swarm 2
Zaris is not engaged
Corban and Rurik are unconscious (and both need to roll death saves)
Zaris may take an opportunity attack on the swarm as it flies past
Zaris, Kaiakas and Reina are up.