I replied to this ask before here, but only addressed the first question while accidentally neglected the second part. So here, the make-up post.
What are Sebastianās skills?
Thereās really not a lot I can say except just summing up the things that happened through out the manga, but I shall try to group them per category. So far in the manga, we have seen Sebastian:
š shapeshift into a whole zoo, not limited to organisms only.
š® conjure food out of thin air (even though it was not appreciated by his master).
šŖ wield muscle strength enough to punch holes through brick walls, contort a metal tank, jump dozens of metres into the sky, drag Finny along with ease like a helium balloon š , etc.
š¤øāāļø display enough agility to dodge any projectile fired at him, be it daggers or 19th century bullets. He can climb and hang from roofs, and do the PHOENIX while holding an injured child in one arm. Speaking of which, he can also dodge the attacks from reapers while holding a child and be injured himself, though he does so with less ease.
š« show astonishing speed in travelling perhaps hundreds of metres within seconds EVEN in human form. The only concrete indication we have of how many km/h he can travel is in the Circus arc in chapter 30, where Sebastian says the following:
Back in the late 19th centuries, most trains travelled no more than 32km/h, and a horse-drawn carriage around 10km/h at most.
Let us be generous and not assume that by āone dayā, Sebas really meant 24 hours. So let us say that their journey would have taken them 20 hours. Let us assume approximately 1 hour lost for getting on and off the train, and getting to the carriage, so that is 19 hours left. In those 19 hours, I shall be somewhat generous and say that 18 goes to the train ride, and 1 to the carriage ride.
(18 x 32km = 576km) + (1 x 10km = 10km) = 586km
So the distance they need to cover from London to Baron Kelvinās manor is 586km. Sebastian can apparently manage that distance in less than an hour, but for calculationās sake, let us take an hour. So if he pushes himself a bit, Sebasā travelling speed in human form can go as fast as 586km/h, which would be equivalent to the small fighter aircraft, the A-36 Mustang.
Still we can safely assume that 586km/h is not Sebastianās top speed even in human form, because he had to carry O!Ciel, and there is only so much g-force a human body can handle. If Sebas does not have to carry a human body however, we can only begin to imagine how incredibly fast he must be.
Also, just imagine how many mosquitoes and other bugs O!Cielās face must have caught while riding Sebmustang.
āļø Sebas can make hyper detailed calculations, is master of more languages than most of us can even name of the top of our heads, has excellent command over art, music, dance, and other such cultural skills.
The most astonishing skill however, is in my opinion his eloquence, be it in normal speech or verbal manipulation in āseducingā vulnerable humans into their demise.
āļø flex his dexterity in re-assembling broken ampules or ripped paper, repair the shattered Phantomhive ring, craft structures as fine as chocolate to anything as majestic as a mansion within no-time, sew an intricate dress from bedsheets within seconds (though his skills are apparently inferiour to Nina Hopkinsā!), and craft items down to nanogram precision (the f*cking cricket ball).
