The Improved Familiar feat is almost a microcosm of the evolution of d20 System options across its most notable RPGs.
In D&D 3.0, the feat didn’t exist under the Core Rules, premiering in the Tome and Blood supplement. D&D 3.5 saw it added to the Player’s Handbook (as well as the SRD), and while it had a few expansions here and there (such as in Dragon #331, which allowed a PC to take the feat and gain an additional ability in exchange for keeping their existing familiar), Pathfinder 1E made its expanded list of improved familiars Open Game Content (just like the rest of the system), making its options much easier to collate.
One thing that’s worth noting, however, is that the Improved Familiar feat doesn’t always require you to take a new familiar in place of your old one. It’s entirely possible for you to take a standard familiar with a template (originally that was only celestial or fiendish, but more possibilities were added over time). While that can be a different creature altogether, there’s no reason to think that this can’t be the same familiar you’ve had up until now, imbued with planar energies that “upgrade” it to a planar being.
Taking that idea further, why not allow for the Improved Familiar feat to augment your familiar in other ways as well? Likewise, why do those template require such strict alignments on behalf of the familiar’s master? It makes sense that you need to be good-aligned to have a familiar with the celestial template, but limiting it to Neutral Good feels too restrictive. Clearly, some tweaking is needed.
To that end, here are my suggestions for alternative options (in addition to simply selecting a more powerful creature) for what Improved Familiar can do:
Upon taking the Improved Familiar feat, if you are at least 3rd level or higher in the class that grants a familiar, you may apply one of the following templates to it (with your alignment requirements as noted):
Advanced, aerial, aqueous, celestial (any good), counterpoised (any neutral), cthonic, dark, entropic (any chaotic), fey-touched, fiendish (any evil), fiery, giant, primordial, resolute (any lawful).
Any abilities which are dependent on Hit Dice use either the familiar’s Hit Dice, or your levels in the class that grants you a familiar, whichever is higher.
Special: If you have a subtype corresponding to a particular template noted above (e.g. the Good subtype for the celestial template, the Aquatic or Water subtype for the aqueous template, etc.), have a familiar, and have at least 3 or more Hit Dice, you receive Improved Familiar as a bonus feat, but only to grant the corresponding template. If you have more than one subtype, you may pick which corresponding template to apply to your familiar; once made, this choice cannot be changed.
At the GM’s option, a template with a Challenge Rating adjustment of +1 or less other than the ones above may be granted to your familiar upon taking this feat.
This allows for a much greater degree of customization, along with a greater range of who can select the various aligned templates for their familiar. Likewise, the special notation allows for characters from alien realms to have a templated familiar without costing them a feat (since otherwise it would be odd to consider, for instance, an efreeti wizard might have to carefully protect a non-elemental familiar on the Plane of Fire until he could earn another feat slot). We’ve also left the possibility open for a different template to be applied if there’s one that’s not on this list but would otherwise be appropriate.
Hopefully this makes your familiar feel a little more new.
Tags: familiar, Pathfinder
Intelligence Check 
January 26, 2022 at 5:06 AM |
Interesting.
Is there anything to stop the PC taking this multiple times, say making a Familiar both Celestial and resolute?
Would you allow variant of this for a Paladin to increase their warhorse?
January 26, 2022 at 8:17 AM |
Thanks for taking the time to comment!
The standard rule about taking feats multiple times is that you can’t do so unless the feat explicitly says you can. For instance, no one can take Dodge several times over to earn a larger dodge bonus to their AC. As such, there’s no taking multiple instances of Improved Familiar in order to start stacking templates on your familiar. You can take it once (either to take an actual stronger creature, or to apply one of the templates here to a standard familiar) and that’s it.
Using this for a paladin’s special mount is trickier. The paladin’s mount gains bonuses as per a druid’s animal companion (which are combat-focused), as well as gaining a few additional powers (including the celestial template at 11th level). As such, there’s a risk of the mount possibly becoming too powerful if you stack another template on it…but at the same time, it’s still just CR +1, so it’s iffy. I’m honestly not sure how I’d go on that one.
January 28, 2022 at 5:31 AM
Thanks for responding!
Agreed that the standard rule is that Feats cannot be stacked, but functionally we are talking about multiple variants – “add Celestial” is different to “add Resolute” (a reason I gave those as an example.
Of course that may not be sufficiently different to justify having both.
The comparison of Druid Companion to the Warhorse is apt; yes, any ruling should cover both examples.
January 28, 2022 at 9:34 PM
While the feat does allow for several different functions, it still falls under the “no taking a feat multiple times unless it explicitly says so” rule. That’s part of the reason why I wrote this as an alteration to Improved Familiar in the first place, rather than a separate feat entirely.
Regarding animal companions and paladin mounts, I’m still having trouble making up my mind. The problem is that, due to their being more combat-oriented under the rules, there’s a greater risk of overpowering the companion (albeit not that much of one). But from a thematic standpoint, it makes sense; why shouldn’t a druid who lives on the Plane of Fire have access to a fiery animal companion? So I could go either way, there.