Combos
Calm, and Backstab: This is your trainer, because it levels Sneak, 1H, and Illusion at the same time. Since they're magically incapacitated, you don't really need to Sneak, they'll just ignore you, but crouch anyway for the EX, and extra damage.
Invisibility, and Assassin's Blade: This is Game Over, once you get this, and a halfway decent dagger, you can kill anything on the ground that you see first. It'll probably get boring after a while, which is why you're also a Spellsword.
Critical Charge: Not really neaded for the Stealth Aspect, but you can Silent Roll, and hold down a Power Attack to leap from the shadows, and strike someone before they have a chance to react. Unfotunately, they patched it so it doesn't work with Backstab multipliers, but I guess it was because it's kind of horrendously OP. Not all that easy to pull off with a Dagger, but if you did, 15x that's damage, guaranteed double critical damage, AND stagger, so efen if they survive, they can't counter while you finish them off. You don't need it with Invisibility, but you're not just a Nightblade, either.
CC, and Disintegrate: Doesn't say it in the tooltips, but this Perk makes lightning lower Heath, Armor, and other resistances on strike. (i heard it was 15%) Followed up by a Critical Charge, it's a 1-2 punch from out of reach that cracks tanks open like a dropped watermelon. Again, even if they aren't killed instantly, they ain't feeling to good, and the Stagger (With a heavier weapon than a Dagger) means you can get at least another hit in before they recover, or run away giggling before coming around for another pass.
Stamina, and Magicka: This is what makes a fully realized Spellsword so unfair. Not as OP as a Stunmer Battlemage, but a lot mor fun to play than standing there in heavy armor, and spamming Impact all day. With a spell in one hand, and a weapon in the other, you can zot them from adistance, then strike them while your Magicka recovers. With Wind Walker, your Stamina recovers faster while you circle straffe, and carpet bomb them with Fire Balls. (Or Flaming Familiar.) Then, another Critical Charge to nail down the biggest target, finish him in a couple swipes, and skip away again... The trick is, one is going back up while the other is going down. Not forever, but this increases your Endurance susbtantialy while that Sorcerer is starting to tap out, and can't run away in all that Heavy Armor.
Ice Storm: This is where it gets kind of wrong. Cold Resistance is very common here in the frosen North, but it's spells have a tertiary (After the secondary Fatigue) effect of slowing whoever they hit that isn't counted by this. Also, Dragons need Stamina to take off, while Trolls (Even Frost Trolls) can't attack at all without it. And finally, this spell travels in a line, sweeping pretty far to either side, while you can kite the enemy into following you so you can hit them all... Extremely powerful with the Hit&Run tactics of a Spellsword.
Flame/Frost Cloak. This is why you got Adept Destruction. You're surrounded by damage over time, plus after effects. Flames keep burning after you run away to come back around, while frost still slows, and since you're sprinting Through the melee with a Critical Charge on the worst enemy, you can also swing by everyone else on the way by, and just brush them with your cloak. Finally, it has a 1 minute duration, so you can cast it, and by the time it wears off, your magicka has had time to recover (If you don't run it down casting other spells.) There may also be unavoidable situations where you can't avoid getting cornered where there's no room to maneuver. there's tight spots in Crypts, and the draugr can sometimes pile on like Mexican skinheads. While this isn't your kind of fight, a Flame Cloak can make up for quite a lot by making sure that Everyone burns (except you, and your follower.)
Hack&Slash and Burn: H&S is a 1H perk that adds Bleeding damage to attacks with an axe. This is why my pure Spellblades (I.E. not hybrid Nightblades) usually use them. It's 3 perks for a maximum of 18 damage over 3 seconds, but that's on top of the Burning status biff left behind by Fire Spells. Like Flame Cloak, which also does 8 DPS. This is in addition to the Weapon's damage, and you don't have to hang around to let them pound on you. Above, I shewed you how you could run through the melee on the way to Critical Charging the boss with a cloak, and burn people En Passant. With a Hatchet, you can keep going while he's still staggered, and he wil Keep taking Damage while you come back around. You already cast your Flame Cloak, and that pass let your Magicka recover a little, so this time, you can lead in with a Thunderbolt, then do it again! It's been longer than 3 seconds, so you re-up your Bleed&Burn, now that's he's weakened to both, chances are by the time you sprint away, and turn around again, he'll have succummed, or you can finish him with a parting shot.
At this point, his friends are probably regrouping to maybe start thingking about putting up some sort of retaliation, but their Boss is dead, some of them are at least singed, and you may have some cover to catch your breath. This is the power of the Spellblade, and if you start off with a backstab first, you can eliminate the Boss outright.
There's your build 8:|