To get the rest of the mini bosses achievements you have to wait for the mini world change Devovorga's Essence in your world.
During a Stage 3 (will begin between 8 and 14 hours after the next server save once Stage 2 is completed)/
Blooms of Doom will now spawn in Devovorga's lair below Vengoth. Kill these with distance attacks because standing next to them will result in your death. Spawns of Devovorga will spawn when the blooms are slain. Kill these and everyone in the area will be teleported to the previous area. Go down the hole again and kill the Spawns of Devovorga again.
The incarnations will now spawn in their lairs again, and for each incarnation that is killed a new Spawn of Devovorga will spawn in her lair. The world must slay these again at the same time as in stage 2. When this is done, all players in Devovorga's lair will be teleported to the area above again. They must go back and slay the Blooms of Doom and the Vulnerable Cocoons. When this is done, Devovorga will spawn again. This time, she will be stronger but not immortal.
Focus all your firepower on Devovorga. When Devovorga is slain, the energy gate in her lair, and all the incarnation portals will lead to the reward room for those who have participated in the event.
Daring Trespasser - Obtainable by entering Devovorga's lair on Vengoth, during the Rise of Devovorga Quest.
Cocoon of Doom - Obtainable by significantly contributing to the battle with a Bloom of Doom
Devovorga's Nemesis - Obtainable by significantly contributing to the battle with Devovorga during the event. NOTE: This is a very rare achievement, only a few people receive it!