[RPG] Starting a campaign at higher level

Short Version:

Maybe P is overwhelmed by bookkeeping and it's distracting him from situational awareness. Help him make a mechanically very simple character without fiddly bits or conditionals to keep track of, so he can focus on making good choices rather than having good bookkeeping. Invite the other players to support P with advice and by being good role models for the behaviour he's trying to cultivate.

Long form answer, with rambling and details.

Back in my very first RPG ever--and also my first time as a GM--I had a player whose poor choices got him repeatedly killed. Let's call him Q.

Q knew the rules and mechanics quite well, but had a very hard time applying them intelligently to whatever situation he found himself in (like forgetting to heal himself as a cleric). Even more than that, though, was his role-playing: he really really liked to role-play his characters, but that got him in trouble because when Q got deep into his character's internal motives the PC would lose common sense and perspective about the surrounding context of his actions.

It got bad. Really bad. Q's second character was killed by the party for betraying them (he had a conversation about his friends over tea with a "nice" lady). At that point I shared Making the Tough Decisions with the group. He studied it carefully, had intense discussions with me about it... and as a direct result his fourth character perished of untempered curiosity: the characterisation "very curious" overcame the common sense "half these items are cursed and my friends are begging me to stop," until the pile of treasure he was investigating yielded up a lethal curse.

After that session I took Q aside and we talked. He knew he had a problem, and he was trying to "get better," but he needed help. I'd noticed that all his PCs so far were mechanically complicated and required in-game bookkeeping: advanced casters and races with lots of conditional features and spell-like abilities to keep track of. So we hatched the simplest possible character build: nothing to keep track of. No "if you're flanking, X also happens," no spells, no per-day abilities. If his character sheet said he could do a thing, he could always do it.

We wound up with a kind of Indiana Jones flavoured skillmonkey (a rogue chassis with homebrew mods to replace things like sneak attack because tracking whether you can deal that extra damage was beyond what we wanted for the build). He wasn't optimised in the traditional sense--but since another PC in the party had straight levels in the NPC Expert class, that wasn't an issue in keeping him relevant in the group. Instead he was optimised for what Q needed: a simple no-bookkeeping character to let him focus on situational awareness and making good choices.

At the end of each session he'd hang back --along with any other players who wanted to-- and we'd reflect on the game: what worked, what didn't. We'd consult (and if necessary research) and come up with what to make sure we did again, and what we'd change next time. (I've since found that any game I run which has some form of this "reflect and plan" dynamic after every session is improved by it.)

In tandem with another player rising to the challenge and being a kind of "teach by example" role model, it worked. A year later Q was successfully running complicated wizard builds with great party dynamics and great depth of character. He was a real joy to work with, and all he needed was to wade in at the shallow end of the bookkeeping pool instead of jumping into the deepest part head-first.

nota bene: My players have tended to treat the group dynamic as one of table-level cooperation between friends. However much their characters may be rivals, at the table they collaborate to tell the best stories, and I'm also one of the collaborators. In groups where players and/or the GM act as rivals at the table level of things, I'm not sure how much my experience will be useful. It sounds like your whole group isn't really on the same page in terms of their desired gameplay experience, and communication isn't really strong. Working on improving the "friends at the table" level of things might help your game in a number of ways.

Masters of the Wild

A ritual to enhance a druid's animal companions appeared in Masters of the Wild (2002), p. 37, a D&D 3.0 book.

Improving a Companion

Some characters, abhorring the prospect of abandoning a trusted friend every level or two, seek a way out of this situation. Long ago, druids developed a magical ritual to deal with this problem. During this ritual, which takes a full day to perform at a holy site or natural glade, the druid's touch imbues one animal companion with additional strength. The druid loses 200 XP, as if she had cast a spell with that XP cost. Only animals with a listing for "advancement" in their statistics can improve through this ritual.

This ritual increases the animal's hit dice by one, which may increase its size once it hits a certain hit dice threshold.

It doesn't change the animal into a dire or legendary creature, but I suspect what you're remembering is the statistics for dire animals and legendary animals, which almost immediately follow this section in the book (p.37 - 43). It's also possible that your gaming group originally misinterpreted or house-ruled the ritual to mean you can upgrade a creature to one of these of equivalent hit dice.

According to the D&D 3.5 Monster Index, there is nothing called an epic or mythic animal in an official D&D product during 3.0 or 3.5. You may be thinking of the legendary bear and legendary tiger, which appeared in the Epic Level Handbook (2002).