- Mathilde: Legendary Lord, our favorite lucky Grey Wizard. As expected she will be a hybrid lord, mixture between a Shadow Caster and an Assassin. Generally the idea would be having her murderize the enemy lord or characters using her stealth and mobility to get close enough while also using her magic for wider support. For unique stuff beyond her gear giving her various boosts (Belt giving her very high spell resistance, Sword being a beat stick and so on). Has the unique ability to swap between an on foot mode where she has Stalk and a mounted mode where she has the increased speed of a horse (even more so than your average mounted unit, making her scary quick)
- Halfling Fieldwarden: Fairly cheap ranged skirmisher, low speed but has the Stalk special rule. Low speed but with a special ability the decreases the range in which they can be detected.
- Longshanks: Hybrid infantry, possess a stalk and a fairly strong ranged attack. Can fight in melee fairly well and they will be rather quick for infantry. Have poisoned attacks.
- Dusk Riders: The Unit version of the proposed plan we have for have for the Apparition binding spell plan. Take the form of Ring Wraith looking cavalry, they are an Elite cavalry option that is Ethereal, fast and designed for brawling combat rather than getting stuck in. Biggest feature of them is perfect vigor, utilization of Crumbling rules rather than fleeing and finally healing while engaged in combat. They are designed to get stuck into an enemy infantry blob and just blend their way through them.
Legendary Lords can basically define their own strategies to an extent (Unless you're playing on the hardest difficulties in which case the only questions are how good they are at supporting the faction's best missile spam unit and whether they're a better spellcaster than a normal flying mounted hero caster.) The Empire doesn't really have melee assassins, the closest they have are the Empire Captain(Can be given a pegasus and used against enemy heroes, but they're more built around helping your other troops to hold the line), the witchhunter(ranged combatant and debuffer, has magic attacks out of the gate so they can kill ghosts) and the Huntsman General(Ranged lord, better against big monsters than human sized characters). So she's definitely bringing something new and interesting.
The fieldwardens are entering into a fairly crowded field, the empire already has Archers, Free Company Militia, Crossbowmen, Huntsmen and Handgunners, all of which are tier 3 or below and many of which are pretty good. They feel like lower tier huntsman, mostly, and might see use in that capacity depending on how they're recruited.
Longshanks depends a lot on their tier, Tier 3 is where huntsman and handgunners live, both of which are already good at the thing they do, they'd probably have to be a smaller unit size but more powerful version of the huntsman, and I'm not sure how much use they would see. At tier 4 they'd definitely see use, and basically be a Huntsman+. I don't know about the balance though, the empire doesn't have any ranged infantry at tier 4 or 5, it's all cavalry and artillery, and the Sisters of Avelorn (High elf tier 4 AP archer unit with decent melee capabilities) are notoriously overpowered in campaign for doing something very similar to what these guys do.
Dusk Riders... I don't think there are any armies currently that have a mix of crumbling and non-crumbling units and I have no idea if that would cause issues, it might be better to just make them unbreakable. The fit's also kind of weird for the empire, imperial cavalry are all shock cavalry(Lightly armored units that will die in melee but can do lots of damage by cycle charging), they don't have any melee cavalry(The sort that gets into melee and stays there) at all, and putting in an extremely high tier one without anything leading up to it feels like a significant shift in capabilities.
The wizard squad idea feels pretty reasonable, the empire has wizard variety as a big thing and likes its diverse esoteric artillery. There are already some units out there which come loaded with bound spells that don't draw on winds of magic, and while those are usually in support of a unit that can also fight there's no reason you couldn't make it the whole point of a unit. It'd probably go in the tier 5 Wizard's tower with the luminarch of Hysh.