Teleporting monsters

Sorry to be a bother, but I've just got one quick question... I want to have a bunch of monsters teleport into a room after the player crosses a certain line. I've seen this done many times before in other wads, but I can't figure an easy way to do this.

All help is appreciated.

Several ways to do it. With doom2, have the monsters stored in a convienient place with their path blocked by a door or lift.
Have the player cross a line which is tagged to the door or lift
sector, and have it open the door or lower the lift. Then the
monsters walk forward and across a line which teleports them to
some destination tagged to their walk-over teleport line.

You typically need to have the monsters facing the general direction of the player, where they are stored, so that they will attempt to go in that direction and over their teleport line when they cease to be blocked. They should not need to have a direct line of sight to the player, and you would not want them throwing fireballs or whatever at you from their storage place I expect.

If you are using zdoom editing, you can have their sector floor scroll to make sure to hustle them over a teleport line, even if they are not attracted to walk that way. They can be unblocked
by raising a door, lowering a lift, or just a line being changed
from blocking to no blocking by script..that's simplest.

With zdoom, you can also choose to spawn monsters where you want them, by script, again triggered when the player crosses some line or hits a switch, whatever. Also can spawn all sorts of goodies, even some weapon fire. Get this...you can have a monster execute a script upon it's death, so when the player kills it, more spawn according to script.

The way that is normally used to ensure the monsters cross the teleport line is to make sure none of them are tagged as deaf. Then you connect the sector they are in with the play area using a small dimensions sector as a corridor connecting the play area and the hidden sector. This corridor need only be only a few units wide and should be placed somewhere you wouldn't normally look. Because of this arrangemant the monsters will hear you, wake up and start milling around. When the door that was blocking their movement opens (or floor drops, whatever) they will walk towards the player so set your hidden, monster supply sector, in a place that will tend to make the monsters walk over the teleport.

I first noticed this on E1M9 of Doom1 but you can see it in many original and add on maps. Go in to MAP01 of Doom2 and go to the big room outside the exit room. You know the hidden room that some imps walk out of as soon as you start shooting in that area? It works on the same principle. The imps hear you and open the door. Go into that little hidden room and look at the top of one of the back corners. You will see the type of small connecting passage I am talking about.

I have found what I consider a slightly more efficient way of doing it, however. If you make the sector the imps are hiding in the same as the sector you will be making a noise in, there is no need to make a connecting corridor to allow the sound through. Simply select all the side defs facing into the room where your hidden enemies are and edit them so those side defs have the same sector reference as the sector you will be making the noise in.

The Zdoom scrolling floor (or a boom type scrolling floor) can have one disadvantage. If the teleport landing is blocked (by you or other monsters for example) monsters will not teleport to it. Or if two monsters cross the same teleport at the same time, only one will teleport. If the teleporting monsters have now been forced over the teleport linedef, they may have difficulty getting back over it to activate it again if you set the scroll too fast. Making sure each monster is in front of a separate tagged teleport line, with carefully placed landings will get round that. The method does work well for making keys or other inanimate objects teleport in, however. If you are using Zdoom, there is always the possibility of using a script to spawn your monsters (or anything else for that matter) instead. The only issue here is that monsters spawning onto the map after it has started will take the possible kill count over 100%. That may or may not bother you.

Hope that helps.

I have solved my problem now.. Thanks to those who replied!

Gotta love the Doom community!