Megalith’s eyes glow with something greater than the will of its master, something akin to self-awareness. This stone goliath sometimes wanders where it believes itself most needed, allowing nearby woldwardens to advance together as a crushing wall while shrugging off enemy attacks.
Megalith is an upgraded Woldwarden. More expensive but tougher, hits harder in melee, has a higher magic ability, and has a much better animus (one that flattens the defense of the enemy).
Megalith is Baldur's personal warbeast, and Baldur2 really likes the healing bond. Both Baldur2 and Baldur1 have decent spells to geomance, and provide free charges.
Lanyssa Ryssyl, Nyss Sorceress or the Blackclad Wayfarer - Hunter's Mark is an excellent threat range extender that provides free charges. And free charges make for some interesting angles in melee.
Bones Combos
Anyone can take him in Bones, which opens up a few more combos. Warlocks with good spells for Megalith to geomance are:
Bradigus Thorle the Runecarver - Rift is a great spell a lot of the time, and the Woldwarden really benefits from Synergy.
Of those, Baldur2, Bradigus, and Krueger2 are the clear winners.
Drawbacks & Downsides
Easy to hit
Expensive
Tricks & Tips
Remember that 5" from Megalith means his aura covers a lot of ground.
Geomancy:
Megalith can boost attack and damage of spells it casts via Geomancy.
Geomancy doesn't require you to "use up" your Combat Action, just to be forced. So you can use it as well as your melee attacks, and/or after Trampling.