Raiden

So this one seems pretty obvious. That hat is just unmistakable.

Like Sub-Zero, Raiden hales from the Mortal Kombat series. I suppose it's not too surprising that there could be two MK characters since Scorpion was the highest selling character in the original Injustice game.

Raiden is probably powerful enough to rival Superman in a fight, being that he is one of the elder gods. Also with Shazam gone, this makes Black Adam the only character that can create a storm.

Black Manta

Like Raiden, this silhouette has some very distinguishable features. That dome head...

This is very likely Black Manta, enemy of Aquaman. His appearance especially makes sense considering that he'll be in the upcoming Aquaman movie.

While Manta does have enhanced strength, he supposedly tends to rely on his suit and technology for fighting.

Likely his fighting style in game will differ from Aquaman's footsies-based play style as NRS tends to make characters that are normally enemies to be very different from one another.

Beast Boy?

For the most part, this silhouette doesn't have much in the way of distinguishable features. It does look to be a bit shorter than the others though.

Many have speculated that this is actually Beast Boy from the Teen Titans. Beast Boy is known for being somewhat of a short character, so it seems to fit.

A character like Beast Boy would be very unique for Injustice 2 or any fighting game as he would have to transform animals for his attacks for him to stay true to his character.

While the character would have a short stature, the hitboxes for his attacks could potentially be huge. This could be a double-edged sword, however, since it would likely increase his hurtbox too.

Clayface? Azrael?

I've seen theories that this character can either be Clayface or Azrael.

Azrael fits because of his somewhat bulky look thanks to his baggy clothing. It would certainly be a unique choice.

For me personally, I'm leaning more towards Clayface. Honestly, you could say Clayface could fit any silhouette thanks to his ability to mold his body's shape but he fits this silhouette in his base form.

Enchantress?

One of the silhouettes is obviously for a female character. Enchantress seems like a good candidate.

This was a character that was pretty relevant in the Suicide Squad movie. As you might expect, she has supernatural and magical abilities.

Wildcat?

This silhouette is a little bit obscured by Sub-Zero but the main distinguishable features appear to be present. In particular, the head and "ears" remind of Wildcat.

I guess we already have Catwoman and Cheetah fulfilling the female catlike characters, so why not a male one?

Wildcat is known for being a great fighter, being that he is a world champion boxer. He is both agile and very strong.

He is also noted for having nine lives due to some magical spell. Not sure how that would translate in terms of gameplay, but we did see how Jason was revived in MKX.

I can't imagine Wildcat reviving nine times during the fight though.