Ad Astra Per Arcana
(Wis; Trained Only)
This skill represents your familiarity with the nature of the planes. You can use this skill to determine basic information about the plane you are on (such as its alignment and elemental traits) or predict when and how the conditions on a plane are going to change (such as gravity, ground stability, etc.) up to an hour ahead of time. This skill is most useful on chaotic planes such as Limbo, where the conditions are constantly changing.
This skill also allows you to sense what plane a portal leads to, and gain an idea of whether the
conditions of the other side are inherently dangerous to you. This can only be done within 5 feet of a portal, and can only determine whether there is a danger from natural conditions of the connecting plane, not whether a creature or trap is waiting on the other side. It does not reveal what the danger is, only that there is one.
Check: You can determine various conditions of a plane or portal.
DC – Task
15 – Predict the conditions of a plane for the next minute.
15 – Determine the elemental and energy traits of a plane, layer, or realm.
17 – You know what plane a portal leads to.
18 – Determine the alignment traits of a plane, layer, or realm.
20 – Predict the conditions of a plane for the next 10 minutes.
20 – You know whether the other side of a portal leads to an environment dangerous to
22 – You know what layer of a plane a portal leads to.
25 – Predict the conditions of a plane for the next 30 minutes.
25 – You know whether a portal is permanent, temporary, or shifting.
25 – Determine basic magic alterations to a specific school of magic or psionic disciplines.
This only applies to universal conditions and not modifications to specific spells.
28 – You know whether a portal is one-way or two-way.
30 – Predict the conditions of a plane for the next hour.
30 – You know the current portal key necessary to open the portal from the side you are on.
Action: Using Planar Expertise is a full-round action. Examining a portal requires you to be within 5 feet of a portal.
Try Again: You may make continuous checks to determine whether the conditions of a plane are going to change. Checks to determine where a portal leads can only be made every hour
Adapted from the Planescape Campaign Setting on Planewalker.com