Perun
Mushroom
I tried this on the WotC boards, and so far got no response. I also posted a similar question a couple of weeks ago, but also got no responses. So, let's give it another shot 
In our current FR campaign, I'm playing a tiefling wizard. He just reached 3rd-level, and took the Improved Familiar feat. Since the character is shadow-themed, I'd like the familiar to have some connection to the shadows as well.
So far, I think I'll choose between a standard familiar with a shadow creature template (from MotP) applied to the tiny viper; or a shadow asp (from the FF, although I'd have to wait till 5th level (at least) for that one).
My DM and I talked about this, and we'd like to hear how other people ruled on a couple of things.
The Improved Familiar, among other things, says:
How would you handle the familiar's poison ability (if it has it)? Most, if not all poisons, use the following formula to determine its save DC: 10 + 1/2 racial HD + Con modifier. The familiar's HD is equal to it's master's character level. Would you consider this to be its "racial" HD? (The familiar description (p. 52 of the PH) says: "For the purpose of effects related to number of Hit Dice, use the master's character level or the familiar's normal HD, whichever is higher".)
From the familiar description in the PH, it's clear that the familiar does not receive any additional skill points (beyond those it starts with). Instead it uses it's master's skill ranks, with its own ability modifiers. However, what about feats? Does it gain new feats for every 3 HD it gains? The quote I referred to above could be interpreted in favour of this idea.
How about the ability score increase every 4 HD? It's also an effect related to the number of HD, right?
I'd be inclined to answer positively to all of these questions, but then again, since I'm the player here, I'm a bit biased. My DM says he doesn't see anything he'd consider overpowered with these. (The only concern actually was the poison ability, but the tiny viper would have, at most, posion DC 26 at wizard level 20, with all 5 ability increases put in Con, and a +6 Con item. An imp or a quasit would reach DC 25 (starting Con of 10, vs. tiny viper's 11). Considering that the familiar provokes an AoO (Tiny or smaller) if it attacks, that it has one-half of the already puny wizard's hit points, and that we're talking 20th level here, it doesn't seem like all that much.)
I'm really interested in hearing your opinions and rulings on this.
Thanks in advance.

In our current FR campaign, I'm playing a tiefling wizard. He just reached 3rd-level, and took the Improved Familiar feat. Since the character is shadow-themed, I'd like the familiar to have some connection to the shadows as well.
So far, I think I'll choose between a standard familiar with a shadow creature template (from MotP) applied to the tiny viper; or a shadow asp (from the FF, although I'd have to wait till 5th level (at least) for that one).
My DM and I talked about this, and we'd like to hear how other people ruled on a couple of things.
The Improved Familiar, among other things, says:
Does the "otherwise use the rules for regular familiars" bit means that templated regular familiars still provide their masters with a feat's worth of bonuses (+3 to one skill, +2 to one save, or +3 hp)?Improved familiars otherwise use the rules for regular familiars, with two exceptions: If the creature's type is something other than animal, its type does not change; and improved familiars do not gain the ability to speak with other creatures of their kind (although many of them already have the ability to communicate).
How would you handle the familiar's poison ability (if it has it)? Most, if not all poisons, use the following formula to determine its save DC: 10 + 1/2 racial HD + Con modifier. The familiar's HD is equal to it's master's character level. Would you consider this to be its "racial" HD? (The familiar description (p. 52 of the PH) says: "For the purpose of effects related to number of Hit Dice, use the master's character level or the familiar's normal HD, whichever is higher".)
From the familiar description in the PH, it's clear that the familiar does not receive any additional skill points (beyond those it starts with). Instead it uses it's master's skill ranks, with its own ability modifiers. However, what about feats? Does it gain new feats for every 3 HD it gains? The quote I referred to above could be interpreted in favour of this idea.
How about the ability score increase every 4 HD? It's also an effect related to the number of HD, right?
I'd be inclined to answer positively to all of these questions, but then again, since I'm the player here, I'm a bit biased. My DM says he doesn't see anything he'd consider overpowered with these. (The only concern actually was the poison ability, but the tiny viper would have, at most, posion DC 26 at wizard level 20, with all 5 ability increases put in Con, and a +6 Con item. An imp or a quasit would reach DC 25 (starting Con of 10, vs. tiny viper's 11). Considering that the familiar provokes an AoO (Tiny or smaller) if it attacks, that it has one-half of the already puny wizard's hit points, and that we're talking 20th level here, it doesn't seem like all that much.)
I'm really interested in hearing your opinions and rulings on this.
Thanks in advance.