Portals-like spell; requesting feedback

[Madeiner]

Hi all.
I'd like to request feedback about this spell i've designed.
It is borrowed from Portal - the game.

As a note, in my campaign all teleportation magic does not work (planes are not correctly aligned, and teleport and the likes send you thousand of miles into space).
However, fluffy wise, this spell, having a definite entry and exit point, might work. (I like physics and mathematics to be the base for magic)

I'd like comments and a suggestion for it's spell level. I'd like to keep it around level 4 or maybe 5.

Spell text following:

Triss' Dimension Portals

Conjuration (Creation)

Level: ?
Components: V, S, M
Casting Time: 1 standard action
Range: Medium
Target: Any flat portion of material at least 5x5 feet in size
Duration: 10 min/level or until discharged; 1 min/level; See text
Saving Throw: None or Reflex negates
Spell Resistance: No
Focus: A tiny replica of a pearled gun (100 gp)

When you cast this spell, you gain the ability to conjure a pair of portals. You retain this ability for the listed duration, or until you have conjured two portals.
Launching a portal is a standard action. If you so desire, you can launch one portal as part of the casting.
To launch a portal, you point your finger at a flat surface within range. A glowing, pea-sized bead streaks from the pointing digit and, unless it impacts upon a material body or solid barrier prior to reaching the desired surface, blossoms into the portal at that point. If you attempt to send the bead through a narrow passage, such as through an arrow slit, you must “hit” the opening with a ranged touch attack, or else the bead strikes the barrier and discharges without effect.
Once a portal is in place, it lasts for 1 minute / level. Until both portals are in place, they are a like a closed window into nothingness. When both portals are opened, a link is enstabilished between them via the astral plane. You and anyone else can freely pass between the two portals simply by traversing it. Each portal is like a window to the other; you can see and hear through one portal to the other, but magic effects cannot pass through, as they are too unstable to allow magic to pass.
When traversing the portal, you keep your momentum and speed. For example, if you open a portal down a 50-feet deep pit and jump inside, you will be launched at great speed upon exiting the other portal.
If you position the portal so that upon exiting one, you are forced to enter the other (for example, by placing them on the ceiling and floor), you continue to gain momentum as if falling, unable to break free, until the portals eventually expire. In that case, you have a 50% chance to simply land on the floor (and take appropriate falling damage) or to be left inside the passage, leaving you stranded in the astral plane.
There is no material space between the portals. Poking an arm inside one portal results in the hand appearing from the other. Should the portal close while a creature is in transit can result in severed limbs or bodies.
Unwilling creatures forced through the portal or accidentally stepping on it, can attempt a Reflex save to avoid traversing the passage, and you cannot open a portal if there is a creature or object standing above the surface to be used.
The portals can be dispelled by Dispel Magic; a creature affected by Dimensional Anchor or similar spells is not able to traverse the portals.

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I was also thinking about possible abuses (my player will try for sure)

1) Ready action against charge, and open a portal just before the BBEG steps over and send him into continous falling, plinking him with arrows while he falls. Basically a possible save or die.

2) Make a portal on the floor and cover with an illusion. Place exit somewhere dangerous. Use as a trap. Not really sure it is an abuse.

I was thinking of changin the whole "fall accidentally" to flat DC 15.

 

[Greenfield]

Well, you talk about the "passage" one might be trapped in if in transit when the spell expires, then in the very next sentence/paragraph you say that there is no passage, no space between the portals, that sticking an arm in one pokes it out the other.

To me, that's odd.

If your DM has banned Teleport (and I'll presume there's a good reason) because of the "planes being misaligned" or some such, why would your cross-planar subway system work any better? Teleport doesn't normally grant any access across planes, and your version seems to do exactly that.

Other than that, it strongly resembles Ring Gates.

 

[Madeiner]

Well, you talk about the "passage" one might be trapped in if in transit when the spell expires, then in the very next sentence/paragraph you say that there is no passage, no space between the portals, that sticking an arm in one pokes it out the other.

To me, that's odd.

If your DM has banned Teleport (and I'll presume there's a good reason) because of the "planes being misaligned" or some such, why would your cross-planar subway system work any better? Teleport doesn't normally grant any access across planes, and your version seems to do exactly that.

Other than that, it strongly resembles Ring Gates.

The wording may be a bit off, as english is not my main language. What i meant is that you do not have to travel in extradimensional space while traversing a portal. There is 0-distance between the two points. You are almost never "in transit" unless you specifically hang there in the middle of the passage. In that case, should the portal close, you get split in two.

I'm the dm; teleport doesn't work because (in my interpretation) it sends you to the astral plane, moves you there, and makes you reappear (by visualizing location) somewhere else. However, "somewhere else" on the material plane is NOT where you think the place is relative to the other planes.

If you instead build a planar "tunnel" by opening an entry and exit point, then, no matter what "direction" you take in the astral plane, you still end up ad the exit, since that's the only way possible.

It's mostly fluff anyway

 

[Greenfield]

To quote your original...

If you position the portal so that upon exiting one, you are forced to enter the other (for example, by placing them on the ceiling and floor), you continue to gain momentum as if falling, unable to break free, until the portals eventually expire. In that case, you have a 50% chance to simply land on the floor (and take appropriate falling damage) or to be left inside the passage, leaving you stranded in the astral plane.
There is no material space between the portals. Poking an arm inside one portal results in the hand appearing from the other. Should the portal close while a creature is in transit can result in severed limbs or bodies.

The first paragraph talks about being "left inside the passage", and stranded in Astral space.

The second paragraph pretty much says that that can't happen, because there is no space between the portals.

That's what I was talking about.

Other than that contradiction, go for it. Of course, it makes long distance transit pretty much impossible, since both portals have to be within the reach of the caster (medium spell range).

 

[Madeiner]

Thanks again for the reply

You are actually right about the contradiction. I didn't think that either you get severed or you stranded in astral space. Either way, you need to use the spell with care.

Yes it is meant for short distance travel. What level would you put this spell?

 

[frankthedm]

What level do you want the characters using this?

By removing Teleport and related spells, you have removed the measuring stick for comparisons. Using the PHB's spells as a measuring stick, ANY teleportation should be 4th level or higher, precedence Dimension Door. This also can move countless people with the 1 minute per level duration. Heck, the closest spell to this is Gate and not even Gate can allow same plane, only works for round per level AND Gate requires concentration.

Another thing about this spell is it vastly reduces the danger to the PC who otherwise would be Climbing or Flying alone and vulnerable while the allies were a distance away.

Most potent thing though is the users can go back through the portal. If it was opaque and one way, it would be a LOT less potent.