Malekith isn't a slouch in the magical department either.
He can banish a Keeper of Secrets with one spell, and seriously hurt N'kari, the greatest of Slaanesh's Greater Daemons:
Malekith did not so much as break stride as he jointed the battle. With a flick of his fingers, he sent a wave of black fire through the Daemonettes who beset the spearwalls, filling the air with the rancourous stench of charred Daemon-flesh. After another few steps, Malekith pointed his arm towards a Keeper of Secrets and clenched his iron first - the beast bellowed in agony as every bone in its unholy body snapped at once.
With a last, lingering smile, N'kari began to squeeze, but the Witch King was not yet done. For the last few moments he had marshalled his sorcery, and now he unleashed it in a single display of devastating power. A bolt of black lightning arced from the sky and smashed into the Greater Daemon, shattering his defences and wreaking ruin upon his flesh. As N'kari staggered with the impact, Malekith burst free of his grasp. Before the Daemon could recover, he brought the Destroyer around in a might two-handed blow that severed N'kari's foul head.
-Armybook: Dark Elves (8e)
He fought N'kari in the Realm of Chaos and while he lost he survived the experience and escaped back into the material realm:
With a triumphant howl, N'kari pushed on through to personally confront Malekith on the steps of the Black Tower. As the Greater Daemon closed with him, Malekith laughed for the first time in many long centuries. When he had last fought N'kari, it had been beneath the walls of the Marcher Fortress in the Realm of Chaos. There, the Daemon had been at the peak of its power, whilst the Witch King had been near death. Now the tables were turned, and Malekith was determined to take his own revenge.
-Armybook: Dark Elves (8e)
Defeated Prince Eltharion (one of the major heroes of the Asur and capable of using magic himself) with a single word:
Malekith had little doubt he could slay the young warrior, but he would not grant Eltharion the satisfaction of honourable combat. Pointing his armoured gauntlet at the High Elf hero he uttered a single word. In an instant, Eltharion felt the darkness surround him, he clutched at his throat unable to breathe. His entire body coursed with pain, as though his blood had been turned into molten lead, tears of blood pouring from his eyes and he fell to his knees in agony, his Fangsword slipping from his grasp.
-Armybook: Dark Elves (6e)
Earlier, he managed to summon and bind N'kari:
N'Kari considered the Witch King. As mortals went, he was impressive. His massive armoured figure radiated power and not unjustified confidence. The spells he had woven were well-constructed, a trap that it might take N'Kari millennia to escape from.
He had already spent too much time in this pathetic place bound into the Vortex. In mortal form, ennui would press as heavily on him as any other resident of this time and space. He felt sure that he could free himself eventually, but it might be easier to appear to give the mortal what he wanted. He was also sure that, in the long run, he would find a way to turn the tables on the arrogant fool. He always did.
'State your terms,' N'Kari said. The Witch King laughed triumphantly. Laugh away little mortal, N'Kari thought. I will have the last laugh.
'Extend your arm,' said the Witch King. N'Kari complied. Perhaps his foe would be foolish enough to break the magic circle binding him… Bracelets and chains snapped into place. The most powerful binding spell N'Kari had ever experienced snapped into place with them.
'Now you truly are my servant,' said Malekith, unable to keep the satisfaction from his voice.
N'Kari wanted to howl with rage, but the spells binding him would not even allow him that.
-Sword of Caledor
Teclis at the battle of the Finuval Plain considered Malekith a superior spellcaster to himself, and felt certain that he would lose if he didn't bypass Malekith's defences by using the Fires of Asuryan against him:
Teclis felt the cold power of the Witch King grow. Malekith had begun to summon the winds of magic to him and sculpt them into a massive, cold storm front of power. Gone was all attempt to subtly shape things. Now he was building a spell to smite his foes down with all the force of a hammer wielded by a god. The skies turned black. Strange polychromatic lightning danced along the underside of the clouds. The fingers of the wind tore at Teclis's cloak.
The winds of magic spiralled in around Malekith, forming a cyclone of power. Teclis exerted his will to counter the spell, twisting the currents out of shape, making it ungovernable, poisoning the structure of the spell even as it was created so that it would become unstable. His hope was that Malekith would try and cast the spell and it would run out of control, but the Witch King understood too well the ways of sorcery.
He gave up all attempts at forming the massive attack spell and sent lines of force racing back along the currents of Teclis's own weaving. Teclis had only a few heartbeats to counter them before bolts of scarlet lightning impacted on the wards he had set. He ground his teeth together with the effort of parrying the bludgeoning stroke.
Sweat stood out on his brow. He cursed himself for over-confidence. Until this day he had not encountered a magician who was beyond his strength and skill to cope with.
He had never encountered anyone as powerful as Malekith. He had a real battle on his hands, and he felt certain that if he continued to fight at this range, Malekith would win. The spell that he had been counting on to smite the Witch King with could be used only at close range, and there was a massive army between him and the blasted hillside upon which the Witch King stood.
'Do you think you are stronger than me?' Malekith asked.
Teclis knew he was not. At best, he was Malekith's equal in power and he was far inferior in knowledge and skill. All the things Tyrion had said when comparing himself to Urian were just as true for him when he compared himself to the Witch King. More so. Malekith had had millennia in which to perfect his arts.
Teclis invoked the power of Asuryan. He reached out with his will and called upon the flames that burned within the Witch King's body. They blazed up in response to his spell. The wards woven into Malekith's armour could not protect him against the attack from within.
'No!' Malekith's voice boomed across the battlefield. Teclis called upon the full power of the Moonstaff of Lileath, using it to sculpt all of his power into one massive bolt of ravening destruction, knowing the pain of the awakened flame within his body would keep Malekith from countering. Malekith however surprised him.
As the titanic bolt smashed home, he spoke a potent spell. The massive armoured form vanished, leaving an outline limned in fire and the web of energies collapsing around him. Teclis
-Bane of Malekith
While Bane of Malekith is a Black Library book, the idea that he was an equal match to Teclis at Finuval Plain is also mentioned High Elves Armybooks (5th-8th at least), and that he exploited Malekith's weakness to the power of Asuryan in the Dark Elves Armybook (8th and 7th). Now, granted that was a younger Teclis at only 145 years of age who hadn't reached his full potential yet, but still, it's
Teclis. While he's not the top dog, Malekith still ranks as among the greatest spellcasters in the setting, and wizardry isn't even his only focus.
Frankly, Malekith terrifies me far more than Morathi, which is as it should be considering this is the guy who managed to keep the Druchii going and under his thumb for five thousand years seemingly purely on his personal power.
