To acquire this GF, you need to farm the following items.
1 x Solomon Ring
6 x steel pipes
6 x Malboros Tentacles
6 x remedy+
Solomon’s ring
This is found at Tears Point in the Esther region.
Steel Pipes
These can be mugged from Wendigos or refined from Elastoid cards. Wendingos are found at the following areas;
Galbadia - D-District Prison
Lallapalooza Canyon
Wilburn Hill
Great Plains of Galbadia (on desert ground)
Rem Archipelago
Gotland Peninsula
Monterosa Plateau
Yaulny Canyon
Hasberry Plains
Roshfall Forests
Obel Lake
Shenand Hill
Ultimecia Castle - Stairway Hall, Passageway
Malboros
Tentacles are obtained by defeating or mugging Malboros. You can also use Quezacotl's Card Mod to turn acquire one Malboro Tentacle from four Malboro cards. Malboros are found at the following areas;
Island Closest to Heaven
Island Closest to Hell
Esthar - Grandidi Forest, Abadan Plains, Sollet Mountains, Nortes Mountains, West Coast, Great Salt Lake
Ultimecia Castle - Clock Mechanism Room, Wine Cellar
Remedy+
These are easy to acquire you must simply use Alexander’s Med-LV Up ability to transform 10 Remedies into One Remedy+. It’s worth noting you must learn Med Data first
When you have all of these simply use the ring that is in your inventory and Doomtrain will automatically join your team. Cheev will pop straight away.