Finding a good group of people online to do the easter egg or achievement “Little Lost Girl”, can be a hard. It is completely possible to complete it solo, so here is a brief guide on how you can easily get it. For the most part it’s easy to do just make sure that you save zombies towards the end of the round so you can run around uninterrupted, for the most part, and complete the staffs.
By the end of round 9 – You should have all the staffs assembled, their riddles completed, and have them in the crazy place ready to be upgraded. Make sure the zombie shield and maxis drone is built as well. It would be a good idea to keep the fire staff and upgrade the other 3 and then upgrade the fire staff, especially if you didn’t get anything good out of the mystery box. Once the Maxis Drone is built collect all of the yellow disks for a free Magna Collider, as this will make things a lot easier.
Round 13 – This round you should cleanse the Holy Water with zombie souls. Just use your knife for melee and the Ultimate Wind Staff if you get a horde coming at you.
Round 14 – Bring the cleansed stone back to the Talk Station and do the same thing as round 13.
Rounds 15 and 16 – With the normal Fire Staff equipped, use it to fill up three soul chests.
Round 17 – Before the round starts, complete the Fire Staff riddle and put the Fire Staff on its holder in The Crazy Place. Then, run back and pick up the Wind Staff and use it to upgrade the Fire Staff. Step 1: Secure the Keys is complete. Save a zombie at the end of the round so you can put the three staves in the robots and the Fire Staff at the bottom of the Excavation Site. Obviously, this step is very tedious. Step 2: Ascend from Darkness is complete. And now the trickiest solo step to this easter egg… Going to Generator 5, hopping into the center robot, pushing the red button, getting purged and tossing an Airstrike Monkey Bomb onto the seal. Step 3: Rain Fire is (almost) complete. Send the Maxis Drone into the pit… Six Panzer Soldats will rain down… blast them all with the Ultimate Fire Staff. Step 3: Rain Fire is complete!
Round 18 – Fill up the 4th and final soul chest. At the end of the round, shoot the three burning carts with the Ice Staff for the free zombie blood, grab it and run counter-clockwise around Excavation Site and kill the zombie running around it. Pick up the Maxis Drone it drops. Step 5: Skewer the Winged Beast is complete. Now go and grab the Thunder Gloves out of the ritual box.
Round 19 – Go down to the bottom of the Excavation Site to punch Templar Zombies with glowing arms. Have the Ultimate Fire Staff equipped in case a horde comes at you. They drop the stone and pick up the Iron Fist. Step 6: Wield a Fist of Iron is complete. At end of the round, go place all the staves in their holders in The Crazy Place.
Rounds 20 and 21 – Kill zombies in The Crazy Place until the achievement pops up on your screen.
I really hope this guide helps!