npc_blob is basically a unused experimental entity that would have been some gross sludgy monster and would probably look simliar to portal 2's Gel (And it probably would have been like npc_surface but if it would be able to attack)

Npc_blob has a special model usement command to replace its model
If you put 0 in the npc_blob_use_model command the blob npc will be a skull.
If you put it on 1 then it will change into a Watermelon
if you put it on 2 then its just a missing model (unless you already fixed it with this guide)
if you put it on 3 then it will be a missing model... again (unless you also fixed that)
These are the values you can reach but if you put a higher number then 3 then it breaks the game and dosent let you play and you have to task end it with the task manager

So after explaining what it is ill show you how to fix the missing models.
Step 0: Get HLS, Otherwise you wont be able to get the models and textures.
Step 1: Get GCFScape, Why? cuz you wont be able to get the model and textures from the HLS game files for the npc_blob then.
Step 2: Open GCFScape, And at the top left corner of the screen click on "File" and then click "Open"
Now what you wanna search for is the HL1 folder inside the Half-Life 2 folder
Step 3: Open hl1_pak_dir.vpk inside GCFScape, why not the other 2? cuz they have nothing in them,
now once you clicked on it you now gotta click on models,
then you gotta search for "w_squeak" now select all of the files that is relating to "w_squeak" dont select "w_squeak2" doe,
Step 4: Extract the selected files with right click and then click on "Extract" and then search for
"C:\Program Files (x86)\Steam\steamapps\common\Half-Life 2\hl2"
Once you find it then click on "models" and then press "OK" this will now extract the "w_squeak" model into the models file but wait! you gotta add the textures too, otherwise it will be a missing textured snark,
Step 5: To get the textures go back, how to go back?, press the green left arrow at the top left corner
Now once you have done that click on materials and then click on models, now what you wanna find is the "v_squeak" folder
once you find it then right click it and click "Extract" Now click on materials and then models and then click "OK" and then restart the map and then FINALLY you have fixed it!

This part is the same process as part 1, only that instead of "w_squeak" model it is "baby_headcrab" and instead of "v_squeak" texture it is also "baby_headcrab", And now you finally did it you have fixed all of them.

And the guide is finally over. now you probably might be asking "why did you spend like a hour making this guide?" "shouldnt you have something better to do?" or "why would you take this effort into fixing a unused npc that dosent even spawn normally?" i did this just bc i thought that it was cool.
(also i hope you understanded the steps cuz you probably might get confused doing them)