In Gardens of the Moon
Malazan High Mage Tayschrenn had a number of Korvalah demons serving him. Each was capable of leveling a city if they so chose. The Bridgeburner, Quick Ben, somehow acquired one of Tayschrenn's demons and released it in Darujhistan to face Anomander Rake while he and Kalam Mekhar made their escape. Pearl fought Rake knowing it was doomed to suffer an eternity of imprisonment inside Rake's sword, Dragnipur.
In Midnight Tides
The Korvalahrai invaded the realm of the Kenryll'ah via the vast Chirahd River. When it seemed that they would overrun the Kenryll'ah, the latter considered forging an alliance with the Tiste Edur. In return for Rhulad Sengar diverting the river into a rent, which would destroy the Korvalahrai and their fleet, the Edur would gain the services of more Kenyll'rah and possibly one or two minor Kenryll'ah. This bargain resulted in the creation of the Nascent.