I have two requests.

First:
I'm looking for something that stops you using a particular actor in battle unless the rest of the party are dead.
The actor has the database id of 1.
So, say you had 3 people in battle, only the other two could fight, no actions appear for the first character, and actor 1 could only fight when the other two are dead.

Second:
I'm looking for, if possible, a way to add actors to the database (or similar) from scripts in events / common events.
Its for a pet / monster raising system. You find a monsters egg, hatch it, the new monster becomes available as a party member, with its own stats, class etc.
All monsters in a class will have the same stats, char/battler graphics, ie. at level 1 hp will be 550, at 99 it'll be 5450.
If possible could you be able to define stats through the script for each class

Other Scripts / Script Edits
A lot, heres a demo
http://calona.net/pics/Monster-Hunters.zip

Thank you to anyone who can help

Well, since I posted the Last Fighter script here, your first request should be fulfilled, but you can choose which actor shouldn't fight unless the other party members are dead if you select one from the $game_party.actors actor index. This means you can only choose one from 0 to 3 or -1 if you want all heroes to fight against the enemy (default battle system normal behaviour).

You can also change who shouldn't fight by calling the script like this...

LastActor.new = 0 # or 1 or 2, etc., # means this is a comment in Ruby and RGSS

Request #2: Adding characters to the 'Database'? You mean to the party? Or an actual change to the starting database as in the database you edit within the editor?

If you mean like:
The actor database has: Aluxes, Basil, Cyril, Dorothy, Estelle, Felix, Gloria and Hilda... only the default ones.
You fight a ghost and capture a ghost egg (a stretch), hatch it and then, the Ghost Hatchling is added to the actual database of Aluxes through to Hilda.... and Ghost Hatchling.

Typically... no.

You see, when you start a game, the actor database goes through a setup and initialization phase and becomes attached to 'your' game. And when you save your game, that data is stored within the savegame, only to be loaded when you continue your game. So the actor database is pretty much static.

Your best bet is to create and store your pets within the database when making the game. If you are using some sort of party changer system, I would look into a way to store the extra party member's ID somewhere else.

At least, you could design their Class and etc during the design phase.

Well, there are some possibilities through scripts anyway. Something similar to what I do with my Enhanced Equipment system where I store "additional" weapons and armors inside the Game_Party object and save and load them adding them to the database on the fly. I could literally clone that part of the system and do the same with actors... I'll give it a shot.

P.S. there should be around a virtual database script that does more or less the same thing

Okay, try this: Actor Cloning System
It's only a starting point but it should do what you need.