Help with this aberration.

[Yael]

I have this Kython character that my group will have a One-Shot with, the game starts at CR 10, so we must take creatures that do not progress "by character class" (on its advancement table), so I chose to take an Impaler Kython and advance it seven hit dice to have it increase to CR 10 (as an aberration it is supposed to increase its CR by 1 per four hit die added, and at HD 19 it increases to Large size, thus another +1).
For the fluff, I was looking for feats, and I found the poison feats that are for creatures' natural poison (such from a bite attack).

The result at 19 HD, was the following feat selection: Ability Focus (Poison), Deadly Poison, Deadly Spittle, Improved Initiative*, Multiattack*, Power Attack, Spit Venom, Virulent Poison.

*automatic feats

Ending up with a DC 31 Poisonouss bite of 1d6|2d6, its DC decreases to 29 if spit, thought I'm not sure if it also decreases in the 15-ft. Cone, I decided that it was the way that made more sense, so I leave it at 29. It is using the Necklace of Natural Attacks with the Assassination enchantment and a Belt of Bear's Endurance +2 (that should not count against the body affinity table).

Is there anything I could swap for power attack, on a poison-related attack/improvement? Any source is OK, from 1st party to over 9,000th party, as long as it is 3.0/3.5.

[Telonius]

I'd check with your DM about the feats. Back in 3.0, monster advancement was a bit different. As you mentioned, Aberrations only got one Feat per every 4 HD, and many monster types didn't get feats at all. In 3.5, only Mindless (null Intelligence) monsters monsters don't get feats; everything else gets a feat at level 1, another at 3, and another every 3 HD afterwards, just like they were a regular character getting them on the level-ups. If the DM is allowing 3.5 material at all, I'd think that they'd be using the 3.5 feat schedule. If you are using 3.5 monster advancement, you should have seven feats other than the two racial ones, so you're one short.

[Yael]

I'd check with your DM about the feats. Back in 3.0, monster advancement was a bit different. As you mentioned, Aberrations only got one Feat per every 4 HD, and many monster types didn't get feats at all. In 3.5, only Mindless (null Intelligence) monsters monsters don't get feats; everything else gets a feat at level 1, another at 3, and another every 3 HD afterwards, just like they were a regular character getting them on the level-ups. If the DM is allowing 3.5 material at all, I'd think that they'd be using the 3.5 feat schedule. If you are using 3.5 monster advancement, you should have seven feats other than the two racial ones, so you're one short.

You are right, then my point of the thread stands even further, are there any two feats that could I fit here? Poison-related ones? :/

[Telonius]

I'd have a couple of observations. First, you're really going all-in for poison. That's fine, but there are a number of creatures that are just plain immune to it. Also, you need to be able to hit the target in order to deliver the poison. I think you have all the feats that are going to be a specific help to poison, that don't involve Lolth's Caress (which unfortunately requires Cleric levels). I'd actually think about taking Improved Bull Rush, and swapping out one of your Poison feats for Shock Trooper. You already have a bonus on your charge attack. This would allow you to do a lot more damage on a single hit. The Strength damage you deal would help make sure he can't effectively counter-attack if you don't kill him in a single shot.