How Do I Import Custom Monsters

It would have been advantageous if you had linked to the resource for "head monster".

The original DOOM mapping format does not allow new monsters to be added, you can only replace existing ones. Depending on what the "head monster" is capable of you can insert, in your pwad, the sprites in between S_ markers and rename the rotations to those used by the original monster.

Adding new monsters is only possible in ports like GZDoom, which support DECORATE and ZSCRIPT.

17 minutes ago, The BMFG said:

i am using gzdoom for testing and im using zdoom doom in doom

No problem.

Take for example the AgathoDemon from Realm667. Copy all lumps into your pwad

Open the lump DECORATE and add a unique DoomEd number, i added 15555. Then edit your pwad to include the AgathoDemon.

Save your pwad and play in ZDoom.

1 minute ago, Kappes Buur said:

It would have been advantageous if you had linked to the resource for "head monster".

 

The original DOOM mapping format does not allow new monsters to be added, you can only replace existing ones. Depending on what the "head monster" is capable of you can insert, in your pwad, the sprites in between S_ markers and rename the rotations to those used by the original monster.

 

Adding new monsters is only possible in ports like GZDoom, which support DECORATE and ZSCRIPT.

i am using gzdoom for testing and im using zdoom doom in doom

I'll try to help, you need a DECORATE/ZScript lump for it, with the monster's DECORATE/ZScript definition.

But, you still need to keep the sprites in S_START and S_END, 

If you are using SLADE3, you need to find the "new entry" button on the top of the screen, the paper with an "E" on it. Name it DECORATE (If it's a DECORATE definition of the monster), or ZScript (If it's a ZScript definition of the monster), then click on the entry and click on "view entry as text", and there should be big text box that looks like this:

Change the "Text Language", to ZDoom DECORATE/ZDoom ZScript, (whatever you're using) and copy/paste your definition into it, then save it with Ctrl+S,

If you don't understand ZScript and DECORATE, read these for help:

ZScript - ZDoom Wiki

DECORATE - ZDoom Wiki

I'm really sorry if this tutorial is a bad one, I'm not really good with these things, hope these help.