Seraphina's power isn't gone, its being redirected.The substance allows somebody else to use her power. If the person given a link to her powe is killed Seraphina would regain the use of her power.
Seraphina's power isn't gone, just suppressed.She will regain her power eventually, it was never meant to be permanent, its just most people don't survive long enough to get their power back.
There will be a massive Turf War arc at some point.Once all the stuff at Wellston is finally settled and changes are made to the hierarchy system, there will be an arc where the students of Wellston go around battling it out with students of other schools to take over their turf. The reason will be to spread Wellston's restructured influence to other schools.
Terrence is a member of EMBER.It's way too much of a coincidence that the boy's power is invisibility, and it was some invisible person that helped the tracker guy (who might also be an EMBER member) escape the mall fight.
EMBER and the Authorities are one in the same.EMBER is just a government branch that hunts down the Superhero vigilantes that wish to change the Authority's system, as well as dispose of young high tiers who could pose a threat in the future (such as Sera).
Headmaster Vaughn is planning to overthrow the government using his Wellston students.The reason Vaughn is letting John dismantle Wellston's hierarchy, along with spreading his influence to the other kids, is to act as a lesson to his students that they don't have to follow the system established by the Authorities.
Rei's still alive.It's simply too suspicious that a character who was introduced dead has been getting a lot of flashback focus. The reason he's been getting a lot of development, such as the side-story between the 1st and 2nd seasons, is because it's building up the character to an eventual reveal that will show that he faked his own death, and is actually still alive doing behind-the-scenes superhero antics in the current day.
Blyke is going to get hold of the power-up drug, and possibly even use it on himself.Following his second loss to John, Blyke has come to the realization that he's too weak, and desires to strengthen himself in order to stand up to John one day. Getting hold of, and using, the power-up drug that was seen during Remi's superhero missions will help him reach that goal quicker.