Quote: "tall"
Model it to be tall.
Quote: "had unlimited health"
use "entityaddhealth=9999" in it's script
Quote: "could kill you in one hit"
If the player is close, animate it to attack, when frame reaches point of dealing damage use "plraddhealth=-9999"
Quote: "would slowly lumber towards you"
Difficult to do a "slow" walk in FPSC, since Lee hardcoded how fast they move. Just use "movefore"
Quote: "when shot, stumble backwards slightly"
"shotdamage=1" and then "moveback"
There, I've told you how one would go about coding it. Now go about coding it.
The one and only,