Shadow Thief

The shadow thief is a utility class that works best during the night. Every single ability they have has higher than normal mana costs during the day, but lower than average during the night. Ideally, you only want to fight during the night though of course this isn't always an option.

Shadowstep at night is better than normal movement. Not only do you move further or the AP cost, with it being a teleport you ignore attacks of opportunity, difficult terrain and other hassles. During the day, it's a worse Fae Flash. Still usable if you need to teleport, but not worth the mana cost in a lot of cases.

Vanish during the night is a 1 RP hide action. This has some use cases, allowing you to make more attack while taking advantage of the stealth bonus. The use case by itself doesn't change much during the day, as the RP cost is a bigger limiting factor than the mana cost in most cases. 

Shadow Cloak not only gives you a stealth bonus, it also lets you stealth even when you don't have cover or concealment. This makes the Vanish ability a lot more useful, allowing you to stealth in the middle of nowhere, although it requires a high stealth skill bonus. It's a one time cost that lasts until the end of the encounter, so it's still usable even during the day. It's also just good for sneaking into places, especially when combined with Shade Form.

Shade Form is a primarily out of combat exploration tool, though it has some use in combat too by being able to move through enemy spaces. It is almost unusable during the day due to its upkeep cost though.