Tried it out, it's awesome

There are some bad things tho. On transit I somehow managed to get 3 portals, so that 1 teleports to 2nd and 2nd and 3rd teleport back and forth.
Sometimes it seems that I get teleported without going in a portal, and it is possible to get invisible portals, not sure if these 2 are the same. It is possible to make traps (some kill with gravity) with 2 portals, for example 1 on ground and other on low ceiling right above it. From some it's possible to get out if you really try.
If you place 2 on ground in a high area, you keep gaining height as long as you keep getting teleported back and forth, however this can be useful.
Sometimes you get teleported to wrong portals.
Players who disconnect leave their portals behind.
For getting out of map, as this is more like a fun mod, this might not be a problem, but you may change it to have bboxes on the particles so that they can't go to where dretches can't.