Jameson works just as hard as anybody else on the crew, so I don't care one bit that he's actually two dwarfs in a trenchcoat.

Doubleheaders enjoy an incredibly powerful edge in the form of additional actions per round, but suffer from noticeably increased fragility as a trade-off. Despite the name, you don't necessarily need to have two heads to take a level in the Doubleheader archetype- it can be used to represent any creature with two semi-independent parts that work in tandem. If you're interested in playing a large number of ridiculously weak individuals working together, check out the Swarm archetype instead.

Doubleheader Multiple heads.
caret-right Cerberus Three heads.
caret-right Ghidorah Deadly double attacks.
caret-right Hydra Heal faster.
caret-right Kuato Choose which head gets hit.
caret-right Zaphod Don't lose actions.

Doubleheader

Utility plus-circlePolycephaly: You have two heads, effectively making you two creatures that share a single body.

plus-circleExtra Actions: Having two heads means a lot more processing power. You may take three actions per round instead of the normal limit of two, split as you prefer between your two different selves.

minus-circleAction Restrictions: You cannot take more than two movement actions in a single round total. Since both heads always occupy the same location, a single movement action moves both. Attacking a second (or third) time during a single round still incurs the normal double-attack penalty regardless of which heads are doing it.

minus-circleSplit Health: Each of your two selves has its own health pool of Flesh, Energy, and Attention. Unlike a full regular creature, however, a head has a maximum of 3 Flesh instead of the normal 5. When you get attacked, the attacker can choose which of your selves to target. When you receive any effect that restores lost Flesh or Energy, it gets restored to just one head at a time.

plus-circleThe Perks of Being Single: Both heads have access to all the abilities you know, share the same inventory, have the same combat ratings (Melee/Remote/Whelm) and draw from a shared pool of resources (Provisions/Supplies/Mojo). Any attack capable of hitting multiple targets (such as most Whelm-type attacks) treat you as just a single creature and damage only one of your selves instead of both (the attacker chooses which one as usual).

plus-circleHalf Dead: If one of your two selves is reduced to 0 Flesh, they are knocked unconscious and you can only take 2 actions per round until they wake up. Any effect that restores Flesh to an unconscious head will revive it. You do not die until both heads have been reduced to 0 Flesh.

Cerberus

Utility plus-circleTriple Style: You have three heads instead of two, further increasing your total processing power. You may take four actions per round instead of three.

minus-circleAblative Actions: If one of your heads is reduced to 0 Flesh, you can take only 3 actions per round. If two heads are reduced to 0 Flesh, you can take only 2 actions per round.

minus-circleFurther Split: Your heads all have a maximum of 2 Flesh instead of 3.

Ghidorah

Offense plus-circleKing of Battle: Your heads strike fast and furious in well-practiced coordination. When you double-attack during a round, your second attack deals +2 damage.

plus-circleTriple Attack: If you choose to attack a third (or fourth, or beyond) time during a single round, all such attacks deal +5 damage instead of +2.

Hydra

Protection plus-circleRapid Regrowth: Any time Flesh or Energy is restored to one of your heads, an equivalent amount is also restored to the other.

plus-circleAuto-Resuscitate: If one of your heads is reduced to 0 Flesh, it automatically regains 1 Flesh at the end of the current exploration turn at no cost to you so long as your other head survives.

Kuato

Protection plus-circleHidden Mastermind: Your heads are very talented at coordinating, or maybe one of them is simply incredibly protective of the other. When you are targeted with any attack, you choose which head takes the blow instead of the attacker choosing.

Zaphod

Utility plus-circleHyperenergetic: You're always feverishly calculating and processing the world around you with whichever head's not active at the moment, helping you set up all sorts of contingency plans. At the beginning of each round in which one of your heads has been reduced to 0 Flesh, roll a trigger die. If the result is 7+, you may take three (or four, if you also know the Cerberus ability) actions that round as normal despite your temporarily reduced number of heads.