The Book of Gears scaling item bonus list mentions competence bonus to skills. What is the minimum level of item you're going to accept for that, since technically you could just make an item that gives a +1 bonus for several skills at 100 gp a pop (and could technically fit almost all the skills available in just the level 7 item), gaining a bonus to those skills equal to character level on all of them. For a level 7 item, that's +7 to 30 skills for 3000 gp. That's more than a little broken, going RAW, as it nullifies the whole point of skill ranks. So I figure you'd want to impose a minimum, just like on the ability bonuses. Bumping it to +2 should be sufficient, as that becomes 400 gp per skill, meaning a max of 7 skills boosted, though I can also see bumping it up to +3 or so.
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Also, how are you going to rule on limits of the immortality granted by True Fiend? Is it simply not aging, or does it also include not having to eat and breathe like the immortality trait of deities? The standard listing (in Deities and Demigods, also Faiths and Pantheons) describes it as they "are naturally immortal and cannot die from natural causes. Deities do not age, and they do not need to eat, sleep, or breathe." Now, since I'm immortal but not a deity, I just want to know what the bounds are. Many Outsiders are technically immortal (though not all) and extraplanar outsiders don't need to eat or sleep, as mentioned in the SRD, though Native outsiders, like aasimar/tieflings (such as my character) do. However, those native outsiders also don't have a level in true fiend granting immortality, so it's kind of fuzzy.