FINAL NOTES
There are a number of feats that haven't been included in the above posts, for a variety of reasons.
*The Samurai Called Jack (S1E2) included Aku claiming to have stolen the oceans of another world in a different galaxy entirely. Since we don't know any specifics and Aku might have used some of his hi-tech to accomplish the deed, instead of his personal power, I hesitate to call it a feat of his. Particularly because it far dwarfes anything else ever done by Aku.
*Jack Under the Sea (S1E9) featured the undersea city of the Triceraquins, amphibians who were banished to the bottom of the ocean along with their city by Aku, who promised them to lift their city if they captured Jack for him (only to go back on his promise immediately). Not included as a feat, for exactly the same reasons as the oceal stealing incident.ALIEN: My lord, we are the Vadaquas from the Mosconian Galaxy. Our water planet has been pillaged. All the oceans that were once our home are gone. We have searched long to find a planet with oceans rich enough to sustain our people. And your world is our last hope for survival.
AKU: I know of your plight, Vadaquian. For you see, I am he who has taken your waters and the riches within them.
*The Tale of X-9 (S4E11) episode includes a brief flashback in which we see a giant form Aku standing over the collapsing ruins of a modern city. Since we don't know the specific cause of the destruction, it wasn't included above.TRICERAQUIN KING: Due to the nature of our geography, it's not often that we receive visitors. In fact, you're the first. Of course, it wasn't always like this. We were once a very social race. Our people lived on the surface of the ocean and traded with the locals of the mainland. That was, of course, before he came and banished us to the bottom of the sea.
JACK: Aku.
TRICERAQUIN KING: Yes. But that's ancient history now.
*Finally, Aku has shown a couple of times vague (and wildly inconsistent) superhuman senses. In Jack and the Zombies (S3E4), he claimed that he could smell the blood of a hiding Jack (that he immediately eye-beamed his hiding place would seem to support the claim, though), something never shown before or afterwards (including situations in which it would have helped him). Along the same lines, in Jack and the Flying Prince and Princess (S4E8), Aku "sensed a presence" when a hiding Jack removed his sword from its sheath (which would have been useful in a number of situations, including the sword switcheroo nonsense of the next episode).
And with this, the thread comes to an end, at least in regards to Aku himself. If you want to comment anything, now is a good moment.Where are you, samurai? You can run, but you cannot hide, because l can smell your blood.