Spirits are primarily stymied by their poor pool of natural skills. SpiritHeal, its 2nd fixed skill, heals all allies in shadow for a fixed 5 health at 0 ap cost, but does not scale with the user's magic or level, leaving it of limited value in the early game and of minimal to no value in the late game. Its passive ability ShadowTrail onCombatStart can be easily misunderstood; it does not grant the user Shadow Trail, but simply ensures that the Spirit starts combat on a shadow tile. In conjunction with its first fixed skill LifeTap, this allows the Spirit to go into ShadowForm at the very beginning of its first turn.
Heal increases a target's health by 5 or 10% (whichever is lower) and has a range of 3, while GreaterHeal increases a target's health by 10 or 20% (whichever is lower). Generally, though, skills that add shield like the Spirit's Protect (which has 3 range and gives the target 100% shield for 1 turn) will do a much better job in ensuring the survivability of your teammates than healing spells will. Spirits additionally have Cleanse, which can remove ALL temporary status effects from its target for 0 ap, Strengthen, for a 2-turn 50% buff to strength, and ShadowBlast, a basic magic attack that deals more damage the more the target is surrounded by shadow tiles.
Other shadow and lymean species can also easily breed useful skills onto a Spirit. Among Lymeans, pure Lymeans can offer Aegis. Fairies, Seers, and Angels can offer FullHeal. Sirens can offer the immensely useful LightningStrike, which has 10-range, 0 cooldown (can use twice per turn), and deals useful electric damage. Unicorns can shield their entire party with good positioning and MagicGuard.
Among shadow species, the Ghost Taurs ShadowTrail, in conjunction with the Spirits LifeTap and ShadowTrail OnCombatStart passive can make the Spirit into a potent and effective shadow-spreader. For melee-oriented builds, Ghostwings and ShadowLizards can offer Swipe and BackStab, with the latter additionally offering Assassinate. HoleWorms, the elite shadow spirit, can offer the powerful offensive skills MagicPull and BlackHole. OctopusGirls can offer the potent MassCurse, which is capable of cripping entire enemy teams with good positioning.
Spirit growths are fairly balanced, with good magic and mana. They have the highest natural lust resistance and MaxLust among shadow species. Note that like most Lymeans, its DrainMana passive can only steal 1 or 2 mana per attack and cannot realistically keep up with heavy skill usage.
Heal restores 5 health or 10% health (whichever is higher) to one ally for 2 mana.
GreaterHeal restores 10 health or 20% health (whichever is higher) to one ally for 4 mana.
SpiritHeal restores 5 health to all allies for 3 mana.
They have poor verility and fertility. Their beauty is the 2nd highest among shadow species.
They have the same semen capacity as most other shadow species. Like most shadow species, they can be farmed for Dark Matter and have a meager 4 milk capacity.