Whether you're a fan of Shovel Knight or not, he will indeed find his way into Smash Brothers Ultimate according to my sources at Nintendo. From what I know a lot of what he does is tied to his items and moves from his game. There's a lot of details to cover here over this trailer from what I've learned, so lets start.
-Trailer release date is currently set for early September along with the launch of the Nintendo Online Service
-The trailer begins with a cinematic, showing a brawl between Mega Man and Mario
-Seconds later, an anchor lands in between them, having them turn, and as it does it reveals Shovel Knight standing with his shovel raised upwards similarly to the pose made when entering a level
-The next shot is him in this pose with a blue background and his name, with the phrase, "Shovel Knight Gets Digging!", and the "Strike The Earth" theme begins playing
-The next couple of shots are showing off his moveset. Shovel Knight uses his shovel for neutral, tilts, and aerials. He also has a "magic meter" which appears to deplete when he uses attacks that have items, and regenerates upon drinking a "magic potion". Magic max seems to be 40.
-Down aerial has him bounce on enemies he lands on top of
-Up Special is his Propeller Dagger, which will allow him to float back up periodically, appearing to progressively drain his magic when used
-Throwing Anchor presumably as his neutral special, it falls at an arch and appears to do a small stun when hitting
-War Horn, which makes a small circle around him that damages opponents that are in range and knocks them back (downsmash?), endlag seems pretty rough as well
-What I can only assume to be his sidespecial is the item "Dust Knuckles", having him equip these golden gauntlets that throw two punches.
-A neat little detail in the trailer is that when not using his shovel, it appears on his back
-Shield Knight is also seen as an Assist Trophy for a split moment
-At the very end of this trailer Shovel Knight uses his Final Smash, which is a combined effort from him, Spectre Knight, Plague Knight, and King Knight doing a flurry of attacks at high speeds, with a final attack by Shovel Knight where he slams his shovel onto the head of the opponent.