When a player opens up a portal, to teleport or travel to another plain or dimension, the in-between is by default a 'dead land' or dead version of the place they left, a plane or copy identical to it save a few things.
Note: it is important that the GM knows that Dead Lands are always basically identical to the immediate world, meaning the same point in space and time that the PC left, only with exception to the following:
GM rolls a 1d10 to determine what version of the dead land is active:
1 - Mirror Reality: The dead land masquerades as the real reality save a few things up to GM discretion.
2 - Dead Objects: Dead land is identical to reality left, except objects don't respond nor are they able to do anything. i.e. Stephen King's Langoliers.
3 - Gravity: DL is an ultra gravity environment and objects are 1d10 their original weight.
4 - Time and Aging: DL itself is aged by percentile die roll and rolls over 95% incur additional rolls. EM saving throws can stop the aging by PCs counter percentile roll. If the roll exceeds the DM roll, the DL goes back in time by the difference, anti-aging. An additional EM saving throw roll is then made at a -4, as the DL morphs. If it is in excess again, it goes the opposite direction, infinitely until PC has escaped.
5 - Candy Land: DL becomes a mirror of the wishes and carnal and base pleasure desires of the players.
6 - Memory House: DL depicts a house, or hotel, no matter what the environment the PCs left, like a house of the mind where long halls with closed doors contain memories of the characters.
7 - Hotel Reality: The space the PCs left becomes a folded version of that space and time in the form of an inter-dimensional hotel. No one knows why it is a hotel and not anything else that seems to be the hub of reality itself. Many theorize it is a powerful demon God of old, something to do with the city of Gog. They hotel is not resemblant to a Linderian hotel from any known society. It is assumed to be from another time. See Hotel Gog for more.
Escaping or traversing a portal:
Portals are used to travel in space or time or both. They are also used to travel through planes and or dimensions.
Teleportation is travel through space. Time travel obviously traverses minutes, days or years.
Upon escape the PCs experience time loss or distortion. GM must determine how long the PCs have been inside the Dead Land. The following conversion chart is used to dictate what that time equals once exiting the DL.
1-10 - Hours become minutes
11-30 - Days become hours
31-40 - Hours become days
The reality the players re-enter may also be distorted. Roll against this 1d20 under AN score. Failing it results in a percentile roll on this chart:
1-3 - Walls become mirrors
4-7 - Words if spoken out loud change related reality