I find myself stopped up short in my efforts to create a major…well, not antagonist, but let us call him a very shady ally, for my PCs. The individual in question, Mykael the Grinner, is the master of a tribe of elves that favor incredibly toxic poisons, venoms, and chemical compounds. The trouble is that all the rules I can find for these substances (and spells that mimic them!) in 3.5 is highly underwhelming. Thus, I have two questions: are there any published resources that can help improve his lethal concoctions, and if not/in addition to those, does anyone have homebrew resources that they might suggest for such venoms?
As BESW said, don't expect the game system to model reality.
That said, if you need to figure out stats for potato tea...
It's an ingested poison. As the SRD says,
Ingested poisons are virtually impossible to utilize in a combat situation. A poisoner could administer a potion to an unconscious creature or attempt to dupe someone into drinking or eating something poisoned. Assassins and other characters tend to use ingested poisons outside of combat.
So, this really isn't likely to be a major combat advantage. In my view, a cheap and accessible plot-device poison isn't really a big deal. Also, how much exactly do you have to trick the target into drinking? From the sound of it, potato tea isn't nearly as potently concentrated as the expensive fantasy poisons in the game book.
What's the save DC? Something that calls for a DC 12 Fortitude save, for example, is still going to mess up a lot of low-level characters, but most powerful people will be pretty much immune to it.
What's the actual effect in game-mechanical terms? In the real world, it's pretty lethal, but lethal in the real world doesn't necessarily translate to "save or die." A poison that does 2d12 damage could kill a low-level commoner. Whereas a powerful character is just going to vomit it up but survive pretty much unscathed.
I'm not saying you should block the players by going out of your way to make it weak and useless. But don't make a game action super-powerful just because it could kill someone in reality. People were killed with regular ol' run-of-the-mill arming swords all the time. Yet they still do only 1d8 damage in D&D. Players characters and antagonists in D&D very quickly become more like action-movie heroes (or wuxia/super heroes, even) than real-world people as they attain levels or Hit Dice.
Beyond BESW's answer of Savage Species and Serpent Kingdoms containing mechanics that can be employed by lizardfolk but aren't exclusive to them
There's Very Little
Few attempts were made to make Dungeons and Dragons, 3rd Edition lizardfolk interesting, which is kind of a shame, really, for an iconic creature with over 30 years of history.1
- The Player's Guide to Faerûn contains the regional feats Axe Thrower (33), Dauntless (37), and Tireless (46), which, while not exclusive to lizardfolk, are restricted to characters from specific regions, and one of those regions is the civilized lizardfolk marsh city of Surkh. These are... actually pretty good for the right characters, except the feat Dauntless; don't take that.
- Dragon #334's article "Ecology of the Lizardfolk" (52-7) has the lizardfolk-as-a-prerequisite feats Chameleon Blood (56) and Reptilian Healing (57). Both are... unspectacular.
I am unaware of any lizardfolk racial substitution levels published by Wizards of the Coast.
In fact, even DandDWiki lists no entries for homebrew lizardfolk racial substitution levels. There are a few 3rd-party products for those who want more lizardfolk crunch. Mongoose's Slayer's Guide to Lizardfolk contains 4 feats, none of which are exclusive to lizardfolk, and the lizardfolk-exclusive prestige classes stillguard and scaled king, both of which are unimpressive. Paradigm Concepts published Ssethregore: In the Coils of the Serpent, an entire empire ruled by non-product-identity lizard types, for the Arcanis setting; Ssethregore apparently contains feats, prestige classes, and so on, but I've not seen it--maybe someone who has could Comment on it.
In the Player's Handbook (1978) the 7th-level druid spell reincarnate (64) and the 6th-level magic-user spell reincarnate (85-6) could bring a dead character back as even a dryad (!) or an ogre mage (!!), respectively, but neither spell could bring a dead creature back as a lizard man (calling them folk came later--hey, it was a different time). Despite this, the Rogue's Gallery (1980) had Jeff R. Leason's character Phoebus (44-5) brought back from the dead as a lizard man; Jeff Dee's illustration of ol' Phoebus wielding a trident captured my 12-year-old imagination. But I did always wonder how that happened when that actually couldn't be rolled.
In Dungeons and Dragons 3.5 there's only a 1% chance a creature who's the target of the 4th-level Drd spell reincarnate [trans] (PH 270) gaining a new young adult lizardfolk body. There's a higher chance of getting a kobold body than a lizardfolk one. But, y'know, at least there is a chance.