I created a race that detects magic automatically, so I thought I should add a way to (slightly) stealth spells against detection. The DCs below are kind of arbitrary, feel free to critique them. In general, I want it to be harder to disguise a spell than to detect the disguise, but not that much harder. So here we are, a pair of new uses for Spellcraft. I made an essentially identical set of uses for Psicraft, which would be used for psionic stuff. I'm not sure how to disguise item strength, but I'd like a way to do that. Maybe some kind of aura supressing item? I'm also not really happy with how the detection DCs are set, but I'm not sure how better to do that. I don't like an opposed roll, since disguising the spell's strength isn't set that way (though maybe it should be...).

Spellcraft (Int)

{table=head] Action | DC
Disguise Spell Strength | 20 + spell level
Detect Disguised Strength | 23 + spell level

Disguise Spell Strength: You may make a spellcraft check when casting a spell in order to reduce the apparent strength of its aura. On success, the strength of the aura (when checked with detect magic or a similar effect) is reduced by one step (a strong aura becomes moderate, a moderate aura becomes faint, and a faint aura becomes dim). No matter how much the apparent strength of an aura is reduced, it will persist as a dim aura for long as it would normally. For every 5 points by which your check result exceeds the DC, the aura's strength is reduced an additional step. No aura can be made to appear weaker than dim. Disguising a spell's strength is part of the action of casting the spell, and does not increase casting time. Disguising a spell in this manner also reduces its aura strength when scanned by detect evil or similar spells, if appropriate.

Detect Disguised Strength: When examining a magical aura for strength, you may choose to check whether or not its strength is disguised. On success, you know whether or not the aura was disguised and what its true strength is. Checking whether an aura was disguised takes one standard action per aura.