Collaborative Feats
In a number of instances that will be listed in this section, Karnilla has helped in a substantive manner accomplish things that were explicitly beyond her personal power. Her creation of Durok alongside Loki is not included, because it is never clarified whether she could have animated the creature on her own and just chose to give Loki the honours.
Thor 153 - Loki lifts Mjolnir by stealing Karnilla's magic
Exactly what it says on the tin. During the events of Thor 152, Thor falls into warrior madness to curbstomp Ulik the Troll and realizes that Mjolnir is missing at the end of the battle.
As Karnilla explains in the next issue, Loki showed up during the battle, stole some of her magic and, in combination with his own power, was able to overcome the worthiness enchantment and escape with the hammer before Thor and his friends realized he had been there.
As far as I know, this is one of extremely few instances in which Loki has been able to lift the hammer in 616 continuity.
Thor 187 - Loki and Karnilla break Infinity's mind control spell
For those not in the know, there is a weird storyline in which a part of Odin dies. Under Hela's influence, this part of Odin (that gets called Infinity) starts destroying the universe and, at one point, puts the Warriors Three under a mind control spell that effectively leaves them catatonic.
During this storyline, Balder recruits Karnilla to break the Warriors Three out of the spell, but her initial efforts are unsuccesful. However, after Sif points to a reluctant Loki that it is the bloody end of the world and that his usual backstabbing will get him killed, Loki combines efforts with the Norn Queen and together break the spell.
Thor 188 - Loki and Karnilla push back Infinity
The culmination of the Infinity storyline saw various efforts to prevent Odin's dead half from possessing his tranced living self (which was resisting subconsciously) and claiming the totality of the Odinpower.
Karnilla's attempts to wake Odin with her spells failed pretty miserably, but by pooling efforts with Loki they actually managed to briefly force back Infinity.
And anyone who thinks that briefly forcing back someone is a pretty lame feat should remember that this was a bloody fragment of Odin that had been causing destruction in an universal scale for the duration of this storyline.
Thor 188 - Karnilla helps supercharge Mjolnir
The last attempt to wake up tranced Odin in the Infinity storyline also involved Karnilla.
To be specific, she cast a spell to supercharge Mjolnir with the godly power of several of the main asgardians (Thor, Karnilla, the Vizier, Balder, Heimdall, Sif and the Warriors Three) and then launched the hammer towards Odin.
This hit finally woke up the Allfather, who reabsorbed Infinity and then started undoing all the destruction it had caused previously.
Thor 249 - Thor and Karnilla pierce Mangog's barrier
During a storyline in which Mangog impersonated Odin with the help of a rogue Asgardian and amped himself by drawing power of the Asgardians loyalty towards their ruler, he set up a barrier around Asgard's imperial palace to keep Thor out.
Having found this barrier impervious to his best efforts, Thor and the Vizier eventually went to Karnilla's lair and asked for her help, since they considered her the only person with some chance of breaking through.
Karnilla's solo efforts were no more succesful than Thor's. However, by combining efforts with Thor, they were able to puncture the shield long enough for Thor to slip in and discover that 'Odin' was actually Mangog, instead of his father gone nuts.
New Mutants 84 - Tiwaz refines Karnilla's spell and animates the petrified people of Nornheim
The people of Karnilla's kingdom of Nornheim were petrified by a magic dust created by Utgard-Loki, king of the Frost Giants of Jotunheim, at the beginning of the Balder the Brave miniseries. For some time, it was a minor plot point that Karnilla's attempts to undo the petrification of her realm kept failing.
When Balder promised to help the New Mutants defend Asgard against an invasion by Hela, Karnilla did another attempt to revive her people that also seemed to fail. Fortunately, there was someone looking who decided to help matters...
The bearded fellow is Tiwaz. Also known as Buri. Also known as Odin's grandfather. And while, the involvement of such a character generally would make this a non feat, that Tiwaz acknowledges Karnilla as a "fine sorceress" and that he doesn't add power, but rather distributes what Karnilla had already cast suggests that the Norn Queen was overdoing quite horribly her attempts to brute-force the cure for the petrification and that it was more a matter of it being tricky magic to get rid of.