Rpg Maker XP: Event help!

(Before you say anything, I did check the search thingy)

I have a few problems with getting certain events on the map to work.

1) I have the event set to be erased after a certain point, but if I leave the room, or save & quit, it will reappear! How do I make things one-time only?

2) How do I start an event (like a 'Game Over') the very second a timer runs out of time?

EDIT: 3) How do I change the appearance of an event during the event? (like the 'change actor graphic' function, only with events)

Also, how do I count an enemy as 'Immortal'? It says there's a switch for it on the enemy page, but I can't find anything!

Can someone help me without calling me a search-neglecting noob?

1) Switches.  Not hard.  Don't make the event get erased, replace that with set local switch a = on and make a new blank page and set the preconditions to have local switch a on.

2) Never tried actually.

3)Once again using switches.  Use a switch to go to the next page and on the next page use a different graphic.

4) If you want to make an enemy unkillable at one point but killable later, simply make a version of that enemy with 999,999 HP and 999 on both of the Defenses.

2) Never tried actually.

Thanks, anyway.

1) Switches. Not hard. Don't make the event get erased, replace that with set local switch a = on and make a new blank page and set the preconditions to have local switch a on.  

3)Once again using switches.  Use a switch to go to the next page and on the next page use a different graphic.

I'll try that.

4) If you want to make an enemy unkillable at one point but killable later, simply make a version of that enemy with 999,999 HP and 999 on both of the Defenses.

Well, what I had in mind was having an enemy say something just before it died (After it ran out of HP). The program told me to click on 'Immortal' (or something like that) in the enemy's page. Then after it was done talking, change the enemy state to 'Knocked Out'. I found no such switch/checkbox.
Thanks, DeathTrooper. To everyone else, I'm still open to advice here.

2. Make an event on parallel process using the conditional branch to check if the timer below 0 min and 0 sec. Then enter the gameover command in the branch.

you can also use common events...so that they can be used over and over again, so you don't have to worry about it...