One of the players in my group wants to take the "familiar" proficiency. How should this come into play and what sort of familiar's should be available to them. The proficiency just says it is a "magical animal companion" does that mean it is simply a plain animal that is also magical. The player in question is a Zaharan Ruinguard and wants to have a spitting cobra. To me the spitting cobra seems quite powerful as a creature completely under the player's controlled. At low HDs it might just ride on him and spit blinding poison at adjacent targets, or worse jump out and make them save or die. Are creatures like this intended to be easily under a player's control?
I am not an Autarch; my ruling would be that no animal can be a familiar if the “familiar HD” it would have are not at least equal to their normal HD.
A familiar always has half the hit dice of their master; a spitting cobra has 1 hit die, so I would not allow a spitting cobra as a familiar unless the master was 2nd level or higher.
In addition, the spitting cobra has more special powers than a normal animal (its HD is 1*, not just 1). Special abilities are more powerful than proficiencies, most of the time, so I would say that each * takes up two of its class proficiency slots. (A familiar has as many class proficiencies as its master). If the master does not have at least two class proficiencies, than I would say again, cannot select that creature as a familiar.
(As a Zaharan Ruinguard, that would require the character to be 3rd level.)
I’d also probably put a hard cap on these things at some point; no, a grizzly bear is not an acceptable familiar, take Beast Friendship if you want a bear following you around. Off the top of my head I would be inclined to place a hard cap of 3 HD and one special ability, barring some sort of extreme circumstance.
This may help...
http://www.autarch.co/forums/ask-autarchs/more-familiar-questions
IANAA, but the Player's Companion templates have instances of python and viper familiars. Spitting cobras aren't so out of line with those.
If you find you must tone down venom, LotFP has an interesting take: on a failed save you take additional hit point damage. It's still enough to drop most normal men, but quickly tapers off in power against high HD monsters and characters.
The familiar will be a creature appropriate to the
character’s alignment and other powers (as determined by
the Judge).
A strict reading is the GM gets to pick, taking into account alignment and other proficiencies. If you do exercise that though, give them something cool. I've played in versions of D&D where a familiar is either useless, or an outright liability. And the question I have in hindsight is... why? It's not the end of the world if a PC uses an ability to win an encounter. There's always more encounters.
The one familiar I've handed out so far in ACKS is a zombie hand. Actually the player picked that out of a short list of options that included cobras and pythons based on the coolness factor, though I didn't provide stats, which it sounds like your player might have been looking at to pick.
I can't decide whether the vagueness in the rules about familiars is a strength or weakness. I have a player who is running an elven spellsword who wants a small totoro as his familiar. (If quasits and imps can sometimes be a familiar then why not a small totoro?) Compared to the stereotypical animal familiar that often can fly this totoro is a small humanoid who will be a fully functional tool user with a bone saw in tow to help with its healing proficiency checks. In this case should the ability to use tools not count as a * ability? Honestly, I'm not sure.
I might handle it by imposing a reaction roll penalty to people who encounter the spellsword with his totoro. It's one thing to have a "pet" raven or viper but when someone has a tiny humanoid with a bone saw that's freaky....!
As far as HD, my house-rule is that creatures scale down in size and strength, which includes damage. A hatchling dragon, at 2* HD, has a claw/claw/bite of 1d2/1d2/2d3. For a level 1 player, the max HD is 1/2, which means his (white) dragon familiar is only 1/4 the size of a hatchling. That gives it a claw/claw/bite attack of 1d2-1/1d2-1/1d3-1, a breath attack that can make an ice cube (no damage), no spells, and an AC of 1. At 1 HD, it'll have 1/1/1d3, a 1d3 breath attack, no spells, and an AC of 2.
For a creature that spits, bites, breaths, or what have you, I would rule that it either does temporary damage (blindness for 1d4 rounds, say), or that it doesn't gain that ability until it is larger.
Remember that familiars have a downside, too; killing a familiar has the potential to reduce a player to 1/2 HP, from full. It only takes one mook getting blinded for everyone to gang up on the familiar - a familiar with only a handful of hp and a pretty low AC, too - and hey, bonus, you also reduce its owner to half hit points!
I think one could use the new rules in L&E to build a new set of mechanics for animal companions and familiars. That's probably a good article for Axioms, really.