Welcome to this Lores post and like all it will break down into my thoughts on the Lore Attribute, the actual spells and then which ones you hope never to get. Although I am sure some are just situational and you need the perfect storm to get the most out of them.
Lore Attribute - After successfully casting a spell, the wizard may switch places with another friendly wizard within 18″. Only handy IF you need to get one important wizard out of harms way or get LoS to use a spell the other one has etc.
Now time for the spells.
Signature Spell: Melkoth’s Mystifying Miasma – Not a bad spell pick any one of WS, BS, I or M to reduce by random amount (while extra version does them all). Although random this can really help especially making combat units almost useless for a turn.
Steed of Shadows – Nice way of getting a character out of harms way but nothing more since you cannot charge with it. Interestingly you could move 2 characters around due to the attribute.
Enfeebling Foe - Hex that reduces a units strength (remains in play). Means enemies struggle to wound but they still can on a 6 generally.
Withering – Like Enfeebling Foe but effecting toughness this time. This is more useful for when standard infantry are in combat as anything would struggle with reduce toughness especially with average being 3/4.
Penumbral Pendulum – A nasty direct damage spell especially against low I armies/targets. Although this balanced by the random distance of the spell and the fact most low I targets have more than 3 wounds so could survive at least a turn.
Pit of Shades – One of the nastier Vortices as although you still get the scatter but the need to pass a I test or die is just nasty. Again really good against low I such as monsters and Ogres.
Okkam’s Mindrazor – This is one nice unit buffing spell especially for Elves or those that have decent Ld but poor strength. In fact there isn’t much that benefits from this spell.
So the Lore of Shadows is a mixed bag of spells with one of the most wanted spells in the game; now as for the spells I am not particularly overwhelmed with is Steed of Shadows generally I believe if you have a character somewhere you don’t want them you have made a mistake and moving them may only fix that problem short-term at least especially since it would be on its own and targetable since it wouldn’t be in combat.