Krayts feats:
1. In lightsaber combat, he obviously outmatched both Cade Skywalker and Darth Wyyrlok III--Both of whom were 2 of the best duelists of the era, along with Draco and Roan Fel. Krayt was the best duelist of the era by a distinguished amount.
2. Though he chose not to wear it in his final confrontations for an unknown reason, Krayt owned a set of Vonduun Crab armor which was inpenetrable by lightsabers, similarly to Orbalisk armor, though it's mechanisms are different.
3. He killed several Tuk'ata beasts with a burst of Force Lightning during his time on Korriban, and has also crumbled stone with FL. He could use Dark Transfer, which is similar to FL, to insta-kill anyone who he can grab with his hands.
4. He has chucked several boulders at once at Wyyrlok in their final battle, and has overwhelmed Cade Skywalker with TK attacks in their final battle as well. Krayt also has "disciplined" Darth Nihl with TK.
5. Krayt has shown the ability to resist powerful Force Illusions that were created by Wyyrlok's Sith Sorcery, and he was able to use this ability himself--Uttterly overwhelming a Skywalker with his Force Illusions of his greatest fears.
6. Krayt can use Dark Transfer, just like Cade can, to heal both himself and others from the brink of death almost instantly. He's supposed to be as good with this ability as Cade is according to the latter himself, and the latter has healed his own wounds almost instantly in a combat scenario before--Leading me to believe Krayt can too.
7. Krayt has also claimed to have learned Essence Transfer from Darth Andeddu's holocron, but ultimately his will was not enough to overcome Cade's own, and thus he failed to take the latter's body.
8. Krayt, after his rebirth, made all who had ever touched the Dark Side across the entire galaxy feel his very presence, letting all know that he was alive. He did this on a Nexus, but still.