Skink Starseer

The Starseer can be held back near the a defended position with other wizards and a Saurus Astrolith Bearer (the "castle"), teleported around to where he's needed, or can travel behind melee units to dish out damage magic and maintain friendly buffs.  With two casts and access to spells that deal mortal wounds, remove enemy wards, buff friendly melee units or increase a unit's speed and mobility, the Starseer is versatile and powerful.  The warscroll ability Scry the Stars lets it protect key units in the battle from any distance.  It is very efficient to have in any army; it's often worth bringing two of them.

As a unit with a Wounds characteristic of 5 or more, the Starseer counts as 2 models for contesting objectives.

The Starseer is excellent in both Starborne and Coalesced.  In either faction, it has access to great lore spells (though they're a bit better in Starborne) and powerful abilities.  In Starborne, like all Seraphon wizards, the Starseer is a Cosmic Node and generates about 3 CPP each round.

Scry the Stars allows a Skink Starseer to give a 5+ ward to a number of friendly units equal to the round number, each on a 2+, with no range limit, once per game.  Despite it being a once per game ability, Scry the Stars is extremely good!  If timed well, it can set the direction of the battle and win you the game.

It can greatly reduce the damage your key units suffer in a battle, and that advantage of having more bodies to attack and defend can carry forward into the subsequent rounds.  Furthermore, Scry the Stars lasts until your next hero phase, meaning the effect will last through at least two combat phases, or three if your opponent takes a double turn.  This can severely reduce the impact of your opponent's double turn, leaving you with a huge advantage.

Celestial Doom is the Starseer's warscroll spell.  This spell prevents an enemy unit from making ward rolls.  Against some factions, this spell will get little use, but against others, like Maggotkin of Nurgle or Slaves to Darkness, it may be worth casting every turn.  When needed, this spell can be extremely potent to let your damage spells and unit's attack do significantly more damage to the most important target for the turn.  Its 12" range is a bit of a limitation, but the Saurus Astrolith Bearer can boost that to 18".

A Starseer can learn any spell from the Skink Spell Lore of its faction.

A Starborne skink wizard can learn spells from the very good Lore of Celestial Manipulation, which includes some very powerful spells.  Cosmic Crush deals mortal wounds to enemy units, and is particularly effective against large units and units with heavy armor.  Speed of Huanchi allows a non-monster skink or kroxigor to take an immediate hero phase move, which not only increases units speed and threat ranges, but also allows synergies with teleports (normally a unit can't move after a teleport by this spell bypasses that restriction), and prevents enemy redeploys (which can only be done in the movement phase).

A Coalesced skink wizard can learn spells from the Lore of Primal Jungles, best known for the speed enhancing spell, Heavenly Frenzy.  Heavenly Frenzy allows any Seraphon unit to run and charge in the same turn.  Saurus Warriors, Saurus Guard, Raptadon Chargers, Raptadon Hunters, Aggradon Lancers and Hunters of Huanchi (Bolas and Dartpipes) all get +1 to both run and charge rolls if they have a musician, which means both modifiers can apply to the unit's threat range for the turn.

The Starseer is also an Andtorian Locus (since it's a non-unique wizard hero with 9 or fewer wounds), so it can learn spells from the General's Handbooks' Lore of Primal Frost, with two great spells: Hoarfrost and Merciless Blizzard.

And like any wizard, Starseers can learn spells from the Universal Spell Lore.