Plague Assault: As an additional cost... [space] ... Put 2 -1/-1 counters each on up to three target creatures target opponent (or should it be "an opponent" or "your opponents"? You don't make it clear.) controls. Those creatures cannot block this turn.
I think the cost definitely balances the 6 (count 'em, 6) -1/-1 counters being doled out, but the 3 creatures not being able to block is majorly good. Which is bad.
Lich Lord: Creatures you control have enslaved. [space] {B}{B}, {t}: Put 2 -1/-1 counters on target creature. That creature gains enslaved. Gain control of that creature.
Liches are Zombies, not Demons.
The reminder text for enslaved should read: When this creature dies, create a 1/1 black Thrull creature token.
Phalanx Formation reads like it'd stall the game out. Also, you forgot a period.
Enslave allows me to gain control of 1-toughness creatures for {B}. I don't think that's what you're going for. Instead, you might want to rewrite it as:
2BB: Exile target creature. Create a 1/1 black Thrull creature token.
Scouting Tactics should just read: Creatures have hexproof during the combat phase.
Sunstriker Knight is missing a period and is probably too cheap given how busted legacy can be.
I hope these help 