Alright, I just had a crazy idea.
Namely, replace the normal Familiar rules with the following:
Familiar: A Familiar is a special animal friend which many spellcasters end up gaining at some point in their lives; after all, the companionship is quite nice, as well as the other... perks.
You may declare a single Diminutive or Tiny animal as your Familiar; if you do, it gains several benefits. Firstly, its HD are advanced to 1 animal HD, if they did not already; they also use your saving throw modifiers, as if they were an attended magical item. In addition, your Familiar has an Intelligence score equal to your highest mental ability score modifier; they gain 4 ranks in every knowledge skill you have at least one rank in, and gain a racial bonus to all Knowledge checks equal to their Intelligence score. Finally, your Familiar is automatically Helpful towards you; no form of coercion, magical or otherwise, can change its attitude towards you.
Having a familiar is not all fun and games; if your Familiar is killed, you gain a negative level that never causes you to lose a level, and which is not removed after 24 hours. You gain this negative level regardless of whether or not you are normally immune to negative levels; you may only remove this negative level by either having your Familiar resurrected or by waiting a week and obtaining a new Familiar.
You may, at any point in which you learn a new language, choose "Familiar" as a language; if you do so, you and your familiar may speak with each-other as if you shared a language.
As long as your familiar shares your space, you may, as a swift action, allow your familiar to hide "inside" you; its soul is subsumed into your body, causing it to disappear and granting you the Alertness feat, as well as one of the following feats as bonus feats, chosen upon first gaining your familiar: Skill Focus (Appropriate Skill*), Lightning Reflexes, Iron Will, or Great Fortitude. You may release your Familiar's soul as a swift action, causing it to reappear in your space and causing you to lose the above benefits.
*For example, Climb for a Cat, Jump for a Frog, Spot for a Hawk...
