In order to make a zombie spawner, you must do the following three steps. Details for each below.
    1. Setup zombie models
    2. Setup character in asset manager
    3. Setup aitype in asset manager

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Setup Zombie Models
1. Port the zombie model and make sure they all have the right hitbox to them
    http://ugx-mods.com/forum/index.php/topic,8904.0.html

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Setup Character
1. Open asset manager
2. Select character
3. Select New Entry and select OK
4. Enter new character name
         Example: char_zom_tomb_1b
5. For each model group select the browse buttons and locate the relevant model, as applicable.
         For zombies that will not gib, only the Body Model need selected
(note: youll need to copy the name of the model, and paste it in the blanks instead of browsing the model or you'll come across this error )
6. For spawned gib models, youll need to insert the joint name, for example
7. Save gdt and convert current asset

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Setup Aitype
1. Select aitype.
2. Select New Entry.
3. Enter new aitype name and select OK
        Example: char_zombie_tomb
4. Select browse button for radiantModel
        For example, the zombies body model would fit this best
5. Change health to 150
6. Select defaultweapon from weapon
7. Type will remain human unless making a dog
8. In the character1 select the browse button and select the character(s) you just made previously
        For example, char_zom_tomb_1b
        If you want multiple characters to spawn from this, then add other characters to 2 - 8
9. Save gdt and convert current asset

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Verify Spawner Was Made
1. Open radiant, close if it was open during converting assets, and reopen it.
2. Right click 2d area and select actor>your zombie path or name...
3. Enter kvps as you would any spawner

credit: SSPartisan ExecutionerSS

I'm in love! Holy crap I'm going to try this out tomorrow.  I have always wanted to do this and have failed so many times attemting to get this to work.

I'm so happy and excited! 

Thank You Thank You Thank You!!!!

Very informative, where were you two days ago when I figured this out by myself! (Well with make cents telling me I had to make the Aitype and character in assman and not just make the files myself haha) nevertheless brilliant tutorial!

wait... bwc actually knows stuff?

Needs more purple thou. Great info man thx.

I did this for my zombie packs

Advantage to this is you can pick which "types" of zombie spawn where - without scripting

I just tried this out and it worked perfect. Thank you so much. 

I tip my hat to you:

Very informative, where were you two days ago when I figured this out by myself! (Well with make cents telling me I had to make the Aitype and character in assman and not just make the files myself haha) nevertheless brilliant tutorial!

You can just make the files yourself, did it that way on my maps. But this way is easier and probably better if you're planning on having different zombie types in different areas like Harry said.

You can just make the files yourself, did it that way on my maps. But this way is easier and probably better if you're planning on having different zombie types in different areas like Harry said.

I did it by files the last time but I didn't know how to make the spawn in different areas that way I'm sure you can with scripts and make cents told me about ai types and characters

I did it by files the last time but I didn't know how to make the spawn in different areas that way I'm sure you can with scripts and make cents told me about ai types and characters

bwc66930 taught me. I used to do it with scripts. This way is way nicer to work with.

wait... bwc actually knows stuff?

well i'm pretty sure what he knows is way more useful than spawning squid models that are over waw's limits in a box map.

bwc66930 taught me. I used to do it with scripts. This way is way nicer to work with.

wait did i just hear what should never be spoken, let alone outloud? BWC TAUGHT? impossible! i need proof!

wait did i just hear what should never be spoken, let alone outloud? BWC TAUGHT? impossible! i need proof!

Bwc66930 learned how to do it from my friend Nikolai/Partisan Executioner,  And bwc66930 knows a lot about modding also

Bwc66930 learned how to do it from my friend Nikolai/Partisan Executioner,  And bwc66930 knows a lot about modding also

bs he only knows purple and nekos! anything else goes through 1 ear and out the other