Hi welcome

Works on majinis, fat majini and minigun majini.
You have to shoot certain part to activate a prompt.
Shoot the part then go near him and press F.
Head : Straight (high damage)
Arm : Jaw
Leg : ??

That if you execute from the front. If you execute from the infected behind, your character willl perform a different melee strike
Arm : Knee
Leg : Neck-breaker (One hit KO)

Fat Majini :-
Either use stun rod or shotgun, then press F. After that your teammate can chain combo.

Minigun Majini:-
Shotgun to the head then F.
Stun rod dosnt stun minigun majini however.

Shoot the enemy then knife him however this is not recommended because the delay is short and the infected might get far from you.
So the better way is shoot his leg twice so he falls down then knife him. This is only recommed if your surrounding dont have too much NPCs. But the damage done is little, so i prefer to use stun rod in this case.
If the NPC is running, shoot his leg then he will fall down immediately.

Shoot the NPC then use stun rod to hit him.
Another nice thing that i've discovered is, it kinda "paralyze" the virus.
What do i mean by that is, sometimes when you kill certain NPC, they will transform to one of the 3 kinds. Long neck / Shell / Flying monster.
If you kill the scripted to be transformed NPC with stun rod, that will prevent he from transforming and die without transform.

The stun works on normal NPC and fat Majini.
However it doesnt stun NPC like Minigun Majini, Chainsaw Majini and some others .

Explosives weapons such as hand grenade, mine and grenade launcher are good choice to take out lot of NPC because it causes AOE damages. Rocket launcher however only recommend to be use against tough bosses like uroboros.

* Incidenary Grenade
It's not explosive but it's good in causing aoe damage to tons of NPC.

This is a really nice weapon because it comes with 6 different ammo type!

• Explosive
  
• Flame
  
• Nitrogen
  
• Flash
  
• Eletric
  
• Acid

This is what i suggest to use against :

• Explosive : lots of common NPC or bosses
  
• Flame : uroboros
  
• Nitrogen : licker
  
• Flash : transformation NPC(longneck/shell/flying monster)(for 1 hit KO), minigun majini (after you
  blind him , go to him press F to melee)
  
• Eletric : chainsaw majini , fat majini
  
• Acid : licker

* Re6 grenad launcher only have 3 ammo types

For common NPCs, Fat Majini, Chainsaw Majini and Miningun Majini :
Blind then and press F

Long neck / Shell / Flying monster : Blind them for 1 hit KO.

Also works on against

I've discovered this combo somehow
First, you shoot the NPC's head
Go near him
Equip stun rod and hit him and then quickly press F

tl:dr Shoot less. Kick more
Thanks for reading