I should search for the first missing flail, the Byzola Flail Head. This item is a chest drop from a Caroeth battlemage or an enchanted barricade, both of which are found in front of and behind the red portal in Chardok. Alternatively, you can buy the item from a broker.
I should search for the second missing flail, the Dymetreax Flail Head. This item can't be gotten from broker! You must loot it from a wooden chest that drops from a Caroeth battlemage, a Caroeth battlepriest or an enchanted barricade, found near the red portal in Chardok.
Go to the Cave of Fear in Feerrott. Hail the Iksar Othixis at ( -1911, -25, 482 ) Copy/waypoint -1911, -25, 482, who will ask you to find 5 tablets.
Go back to Chelsith and search for 5 clickable tablets. Because three of these tablets can be obtained while invisible, and because they respawn, this stage can be done solo. You can also exit and zone into a new new Chelsith instance after 30 minutes. Tablets are located here:
Near the entrance ( 15, 4, 390 ) Copy/waypoint 15, 4, 390
In a pool ( 162, 1, 250 ) Copy/waypoint 162, 1, 250
At the Shrine of the Deep ( 434, 44, 130 ) Copy/waypoint 434, 44, 130
On the ramp near the Shrine of the Deep ( 346, 16, 148 ) Copy/waypoint 346, 16, 148
In the water below the ramp to the Shrine of the Deep ( 358, -22, 131 ) Copy/waypoint 358, -22, 131
Kill 75 Reet Slaves in Sebilis - either near the sporconids on the lower level, the labs on the upper level, or in the kitchen (look for orange dots on your map when you get close. Best in Slave Caves).
The zone in to the Instance where the final mob (80^) is in front of where the Avatar of Hate( -1307, 48, -1509 ) Copy/waypoint -1307, 48, -1509 spawns. There is an anvil on the ground near that location, click it to zone into instance. (Only Inquisitors on the same step may enter the instance.)