Jiix's powers depend entirely on the state of himself and world, and the nature of his enemy. Particularly, his tactics change when he faces undead vs. living foes.
On any given day, Jiix may start with his bat familiar or an undead servant as his corpse puppet. After resting to regain his spells and abilities, Jiix typically begins fleshcrafting himself and his corpse puppet, if available. Most often he will apply four alterations: advanced attacks, improved natural armor, negative strikes, and versatile attacks. This costs him 4 spell points, or 8 if he also applies these alterations to his corpse puppet. He as the option to change his form in more substantial ways, such as gaining additional limbs or natural attacks, but these alterations will be overwritten when he changes forms with other abilities, so he'll skip them most days. Sometimes he'll add the necrotic bomb alteration to his corpse puppet when he plans on disposing of it in favor of a new one (or to regain his familiar). In situations where he faces a specific challenge, he can give himself a new combat talent (in Athletics, Berserker, Brue, Guardian, or Wrestling) or new skill points (8 per spell point invested in any skill he likes) for a temporary advantage. Fleshcraft alterations only last for 24 hours, but he can apply more throughout the day as he chooses (at an additional cost of a spell point each). His default alterations are already incorporated into his sheet.
Jiix has several unique abilities to transform into a jaguar, a human, and something in-between. In all his forms, he retains his bite attack and the ability to jump great distances. When he uses the Change Shape ability of his skinwalker heritage, he has the option to gain claw attacks, an increase to his speed, or the ability to see in darkness (he chooses one). Let's refer to this as his werejaguar form. He may remain in werejaguar indefinitely, if he chooses. In addition, Jiix can Shapeshift into a full Jaguar, losing his humanoid shape and gaining hind claws, a keen sense of smell (as Scent), and the pounce ability. Let's call this his jaguar form. This requires concentration to maintain, though twice a day he can maintain it effortlessly for 30 seconds or so. He can also assume the shape of other animals when required, or benefit from other bestial reflexes, but he can never assume more than three new alterations this way. Technically, both his humanoid form and his werejaguar form are considered his base form for purposes of interactions with his alteration magic. This means that he can apply the benefits of his werejaguar form to his jaguar form, but not the other way around. For this reason, he will typically cast shapechange under ideal conditions (see below) to enter his jaguar form, and then use change shape to apply the benefits of his werejaguar form. This gives him a bite attack, four claw attacks, scent, and pounce (among a few incremental bonuses). He can always mix and match abilities later when he wants access to a different suite, but this combination prepares him well for battle.
Against weaker opponents or when he benefits from the protection of his allies, Jiix can charge into battle with a pounce as a full-round action. This allows him to attack with all of his natural weapons at once, for a devastating assault with his bite, two fore claws, and two hind claws (five attacks total). He jumps from too great a height, he can always cast his feather fall spell as an immediate action for a safe landing. For the first two battles each day, he'll spend his swift action to extend the duration of his jaguar form (without concentration or additional spell point cost). Ideally, he would strike from above or the shadows, but he can just as equally charge into battle head-on. If he successfully hits with his bite attack, he can initiate a grapple maneuver immediately (rolling his alternative combat maneuver bonus or Alt CMB). If that succeeds, and he maintains the hold until his next turn, he can attempt to swallow the creature whole. Due to the primal magic of his infectious maw, he can even swallow medium-sized creatures. Jiix naturally prefers to swallow living creatures this way, heart and all, to satisfy the needs of his curse.
Undead, however, do not have a beating heart, and so must be dealt with differently. For this, Jiix relies on his spells and supernatural abilities. First, he would attempt to gain control of the undead, either through the Command Undead spell or the Command Undead supernatural ability. The spell has the advantage of potentially being more powerful (see below), but only maintains control for five minutes or so. His supernatural ability to command undead can last for days, but there's a higher chance that undead will resist or escape his control, so he must be careful. Undead he reanimates himself are more reliable, so he should make use of corpses to reanimate whenever possible. At most, he would have four times his level of undead under his control each adventuring day, plus any that he gains temporarily with the command undead spell. Both forms of command undead can be used as area attacks, with slightly different attack profiles to allow him to target multiple enemies at once.
Jiix prefers not to engage in melee when there's a credible threat to his safety. Beyond the obvious reasons, he draws upon his own lifeforce to power his spells, and thus prefers to protect his health total more than others. Commanding his undead minions is preferable, then, to engaging in a chaotic melee. Life magic is a fallback option, as it can help to stave off unconsciousness resulting from the draining effects of his magic, but it is a better option to use after battles. In addition to healing hit points, he can cure many poisons, diseases, and curses. Even when an ally falls in battle, he can attempt to resuscitate them as a standard action, bringing them back from the brink of death if he acts in time (within 1 round). Notably, his familiar can channel his spells through itself, giving him additional range and flexibility.
Out of battle, Jiix is primarily a healer and a scout, although he can serve as the party face with creatures welcoming to monsters. Animals are particularly receptive, and can often provide hints and clues to aid his mission. In addition, he can summon the spirits of the dead to ask for questions or advice.
One final consideration is the optimal casting of spells. Jiix receives a number of circumstantial bonuses to both his caster level and the DC of his spells (how hard they are to resist) based on the state of himself and his environment. His caster level improves whenever he casts spells outdoors at night (+1), in his werejaguar or jaguar forms (or any animal form, +2), or when he casts any Death sphere spell (+1, or +2 for control undead, summon spirit, and reanimate). Additionally, he may attempt to cast a spell as a primitive caster, adding verbal, somatic, or material components to his spells to increase his effective caster level (+1 for each component added). Notably, he cannot speak or perform the necessary somatic gestures in his jaguar form, so this limits his primitive spellcasting. In addition to providing +1 DC for each +2 to his caster level, if he can manage to achieve a total caster level of 7 or higher (base 4 plus 3 from any other sources), then he can make use of Irresistible Spell metamagic. In short, this allows him to spend 4 extra spell points to increase his spell's DC by 10, making it much harder to resist. In order to maximize his effectiveness against powerful enemies, he should make sure to apply his irresistible metamagic while meeting the conditions above. Whenever his caster level is less than 7, he cannot make use of irresistible spell. Likewise, when in his Jaguar form, he can't give orders to any of his undead minions, so he should alternate forms as needed based on the specific needs of the situation. It's assumed that Jiix benefits from at least one caster level increase whenever he casts his shapeshift spell.