First, build KT-4, Zombie Shield and Skull Of Nan Sapwe. If you don’t know how. Here’s the link for KT-4, Zombie Shield and Skull Of Nan Sapwe.
First part, Spider fang. Build KT-4, then Head towards to Lab A all the way at the end near perk machine. Shoot the web using your KT-4 to open the cave. Go inside and kill the giant spider. To kill the Spider, you just going to shot will he is opening his mount. Once he is dead, go towards to his mouth and press action button to get your first part.
Second Part, Special Plant. Build Skull of Nan Sapwe. Next, Get the rainbow water. To get this, you need to use sewer pipe and on the middle of that tunnel you will see a 115 rock. Once you reach that, press action button to get your water. To get the exact location. Check my video below. Next, head over to Living Quarters . Go on the corner where you can get the purple 115 water. Use your Skull of Nan Sapwe and press, hold right click on your mouse ( PC Users) while point out on the wall where there is a half poster. Once the poster reveal the half, Keep holding until you will heard a scream. Thats your cue. Now, go again to the operation room where you’ve got the part on KT-4. Once you reach the bottom, use again your Skull Of Nan Sapwe and point it on your right where there is a flat surface wall. Keep holding right click mouse ( PC Users) until in reveals a secret room. Now, plant a seed and water with rainbow. Do this 2 more executive rounds until the plant is fully grown. On the fourth round your plant is ready. Note: Make sure that you water the plant and if you failed, you have to plant again a seed and redo the steps.
Third part, Special Tube. First, Build a shield. Second, finish your challenges. If you’re playing co-op, all players must finish there challenges. Next, wait until lightning strikes on the altar . Then, quickly use your shield then run toward on where there is electricity. Next, head over to the Lab A and use your shield to electrocute the panel. If you are playing SOLO, just go inside the cage and this cage will automatically go down but make sure you get the part because this cage will comes up in a few seconds. If you are playing CO-OP, one player must go inside the cage will the other will activate the panel. Once you got the part, Ask again to your fellow players to bring the cage by activating again the panel.
To build this, you must go on operation room where you build KT-4. If you notice, there are two machines, One is for KT-4 (Regular) and the other one is for Upgrading. Drop all your parts on that machine and there you have it. You have now the upgrade Wonder Weapon.