If you use "DNA Surgery" and choose Fiend-Type, "Goblin King" increases its attack points by 1000 from virtually every monster on the field.
You can also use "Scapegoat" with "DNA Surgery" to automatically gives this monster 4000 attack points.
By equipping "Megamorph" to your opponent's "Goblin King", you reduce its attack points to zero, regardless of the number of Fiend-type monsters on the field. (Any number x 0 original ATK = 0)
"Phantom Skyblaster" is ideal with this card as it will summon 2 tokens, giving this card 3000 atk
"Goblin King" equiped with "Raregold Armor" with other fiends on the field creates an Instant attack lock.
Use "Zerozelock" to protect this monster when you have no other Fiend-Type monsters on the field.
Use the effect of "House Duston" to special summon to the field, 4 Duston monsters on either side. Not only does this produce a 8000 attack point monster but it also has the potential to lock down your opponent's monster card zones from being utilized.
After this card is Special Summoned (via "Monster Reborn", etc), if its ATK doesn't exceed 1000, you can chain "Inferno Reckless Summon" to Special Summon another 2 "Goblin Kings". Neither of them can be attacked and they will have at least 2000 ATK each because of their effects.