Ultimate towers. Certain combinations of fully upgraded towers now allow you to form an ultimate tower, placing the ultimate tower does not replace your other 2 fully upgraded ones but is merely a requirement to build it. Maybe make it an upgrade but each player is only allowed a maximum of 1 ultimate tower.
Death tower: A combination of the assassin tower and the gravity disrupter, the death tower still benefits from crit and a slowing poision while also gaining annihilation which gives it a % chance to kill a non boss unit instantly
Shieldbreaker: A combination of the magic and lightning tower the Shieldbreaker not only steals mana while attacking with an AOE forked lightning attack but also has an ability that allows you to penetrate divine shield and disable it temporarily, the shield breaking ability has a 30 second cooldown.
Behemoth launcher: A combination of the Stone thrower tower and peasant launcher the Behemoth launcher gains passive poison damage ( like the sluj tower ) while also launching a boulder that has a chance to AOE stun
All ultimate towers gain chaos damage and gain 1 inventory slot? I was going to think of more ultimate towers but I got too tired. will probably edit later. as usual leave a like or comment