We know that the Kingdom Rush expansion will feature new advanced towers.
My guess is that every tower will have only one new advanced tower and not two, as for the developers creating 8 new advanced towers for the expansion sounds like alot, and as a player having four options sounds like too much.
If this is true, the barrack's one has been revealed, being the assasin's tower.
This leaves the question what the advanced towers will be for the archer tower, mages and the dwarven bombard.
Discuss ^^