The 4 trials relate to the 4 wonder weapons in this map, all 4 of them are required for the easter egg/boss fight. The deathraven will unlock the scythe, which is by far the easiest one to unlock.
1. From spawn, make your way to the right to the phylactery. Upon entering this area, there is an altar right in front of you. Press x on it and a 45-second survival will start. Simply run around in this around for 45 seconds, after which the flames will disappear, and revealing the scythe for pick up.
2. For the next step, you will need
- The unupgraded scythe (already acquired)
- A wire, which can be found at spawn, against the wall opposite the teleporter.
- The spine from a void sizzler (new zombie). To acquire the spine, melee the void sizzler with the scythe. (to force, spawn a void sizzler, unlock Pack a Punch and enter the PaP room, every other time you do so, 1-3 void sizzlers will spawn)
3. Now in the Phylactery, there is a large stairway leading up to the bloodpool in the center. Simply place the wire, the spine and the scythe at the top of the stiarway, next to the bloodpool. Now kill about 15-20 zombies nearby until it is charged (you will get a notification).
4. Wait 2 full rounds, at the start of the 3rd round, you can pick the scythe back up. Note: The scythe will disappear from the floor next to the bloodpool, though you do not have it in your inventory.
5. Now head into one of the teleporters to Pack a Punch, which will take you to a similar room instead, allowing you to complete the trial. SImply pick the scythe up from the middle of the room and kill the 3 wustling zombies to upgrade the scythe and unlock the achievement.