Alphadin, you said you are not an expert, did you even play Alien Swarm?
Anyhow, the Shield Bug defends himself when attacked or when he sees a close enemy.
The best result to achieve this is by making the animation of it defending itself would be a crouch animation.
The crouch speed should be lower then it's walking speed, overall it's not a fast unit, but a strong and quite annoying unit.
When it defends itself, you should make the player/bot have the variable %obj.shielded set to 1, then you have to include a script that checks the position of the damage done on the Shield Bug.
When the damage is done from the front, it should be ignored.
I advise you to take a look at the scripts for headshots and of course Space Guy's shield scripts.
Be sure to make the normal walking animation look like when it's not defended and walks.
And the crouch walking animation should of course look like when it defends itself and walks.
If you need more information, you can always ask and you can add me on Steam if you want, my name is Lordician.
For the parasite script, i advise to look at the script for the jockey.
Last, i highly advise you to either make your mod first work with ZAPT, as it would allow you to make it alot better.
In my opinion then.
Or perhaps you should make it work like this:
When server has:
-ZAPT on, Gamemode_Zombie off - Enable ZAPT scripts.
-Gamemode_Zombie on, ZAPT off - Enable Gamemode_Zombie scripts.
-No zombiemod enabled - Enable normal playertype scripts.
If ArmyUnit haven't changed his mind, we are doing this with the BugMods too.
It widens the range of your public alot while not having an independent script for the AI.
But of course, after all you are the scripter, you could just ignore this whole post.