Im not sure if this is a rules question per se, probably more of a spitballing, looking for input thing and I'm not sure where to place that thread.
In my campaign magic items require totemic components to create and also expulse energy when destroyed, a la staff of power but scaled to the potency of the item.
Anyway, upon ousting and forcing into retreat a group which had taken over a major mill, the entirety of which is protected by an anti-magic field, they come across a free standing stone arch and door that the remaining bandits used to escape. The doorway basically contains a dimension door enchantment able to function briefly within the anti field.
The Paladin shouts, "EEEEEEEVIIL" and attacks the portal. Nat 20, max damage, Smite just in case.
Sparks from the blow catch the mill powder on fire doing last damage to portal, portal explodes sending out a coruscating wall of purple flame dealing 5d12 fire damage followed by a dc20 fortitude save to resist the unbound teleportation magic.
Those who failed I had roll 2 d100's. 1 to see if they are affected permanently in some way, 1 to see how many miles from the epicentre they are teleported.
My questions are twofold. 1 as a new DM looking always to improve, does this series of action/ consequence feel fair and intuitive to you?
2. What sort of interesting permanent affect can I give/ impose on the player? It must be based on, or at least related to, Dimension Door.
If you want something a little less convenient for the players you could do something a little more random, the effected PCs will randomly teleport every now and then. Blink dogs shift within 40ft, so D8s work great for randomising this. The effected players will randomly (1/8) teleport at the beginning of there turn. Role a d8 to determine direction and another to determine distance. This gives the flavour of a teleport effect but is more of a detriment then a benefit so the PCs won't want to run around crunching items for powers...
- "the DM is a mystical figure from another plane of reality that can only communicate with us through the magical program known as Skype" - Nasim "Knifey" Val