I'm considering giving my party's mage a Portal Spell as a way to spice up our campaign. The catch is they can only use it twice per day, the target surface has to be flat, clearly visible by the caster, and less than 40 feet away. The portal only lasts about 2 minutes, is 5 feet in diameter, and takes 6 seconds (one full round of combat) to caste for both ends. They can also only have one pair active at a time, and the portal remains completely solid until a second one is activated.
I'm trying to figure out how this would affect the overall game's development. I want this spell to be very useful in some situations, but not become the solution to absolutely everything and hence make the game boring. Since this is a very versatile and mind-bending spell, I wanted to see what some others thought before giving to them (I can always take it away, but I'd rather not have to).
Here's some things it would make trivial:
- getting across a small valley, treacherous river, or spike filled pit.
- getting onto high surfaces that have a roof over them.
- moving heavy objects that the players can push into the portal. Squash the enemy!
- it has a line of effect through it, so you can shoot arrows, cast spells, and thrown things through it.
Does this spell seem ridiculously over-powered? Should I add some additional catches, or give it to them as is? What creative uses that I'm not thinking of might it have?
NOTE: I'm tagging this system-agnostic because my group uses free-form roleplay as our system: we have nearly no stats whatsoever and I resolve things as I see fit, even though I try to as consistent, fair, and realistic as possible. I suppose they would be around level 3 in D&D 4.0 so you can get an idea of how powerful they are, but please don't let that have any significance other than telling you they don't have super-ridiculous spells yet. :D