Can't replace weapons with DECORATE

That code looks fine to me.  Try this, which inherits from the BFG9000 and only includes what is being changed.:

ACTOR YeOldeBFG : BFG9000 replaces BFG9000
{
  States
  {
  Fire:
    BFGG A 10 A_BFGSound
    BFGG BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB 1 A_FireOldBFG
    BFGG B 0 A_Light0
    BFGG B 20 A_ReFire
    Goto Ready
  }
}

Still doesn't work

make a player class that actually can yield any of your added guns, refer to these articles for everything you could need

https://zdoom.org/wiki/Creating_new_player_classes
https://zdoom.org/wiki/Classes:DoomPlayer
https://zdoom.org/wiki/Using_inheritance
 

1 hour ago, Pooh said:

make a player class that actually can yield any of your added guns, refer to these articles for everything you could need

https://zdoom.org/wiki/Creating_new_player_classes
https://zdoom.org/wiki/Classes:DoomPlayer
https://zdoom.org/wiki/Using_inheritance
 

Still doesn't work. From whatever reason code from that tutorial works.

ACTOR YeOldeBFG : BFG9000 replaces BFG9000
{
  States
  {
  Fire:
    BFGG A 10 A_BFGSound
    BFGG BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB 1 A_FireOldBFG
    BFGG B 0 A_Light0
    BFGG B 20 A_ReFire
    Goto Ready
  }
}

Actor DoomPlayer2 : DoomPlayer replaces DoomPlayer
{
  Player.StartItem "Pistol"
  Player.StartItem "Fist"
  Player.StartItem "Clip", 40
  Player.WeaponSlot 1, Fist, Chainsaw
  Player.WeaponSlot 2, Pistol
  Player.WeaponSlot 3, Shotgun, SuperShotgun
  Player.WeaponSlot 4, Chaingun
  Player.WeaponSlot 5, RocketLauncher
  Player.WeaponSlot 6, PlasmaRifle
  Player.WeaponSlot 7, YeOldeBFG

}

Did you add your new player class to mapinfo?

4 minutes ago, Pooh said:

Did you add your new player class to mapinfo?

no. how? and how code from that tutorial works without modifying mapinfo?

There is nothing in that code that would work any better, or worse, than what Empyre posted. That's just how you make a gun. Did you assume it works better just from the text? That was first.

Second, i've send you a link to tutorials on how to add classes, which makes me think you've barelly read anything.

So heres a spoon:

1)Make a mapinfo lump inside your wad

2)Type in (and im going to copy it from the zdoom wiki because you probably wont read anything anyway):

GameInfo
{
   PlayerClasses = "MyPlayer"
}

3)thats it

Third, you've used inheritance, so

Actor DoomPlayer2 : DoomPlayer replaces DoomPlayer
{
  Player.WeaponSlot 7, YeOldeBFG
}

Should be enough