[Item Concepts] Banner of Command + Noxian War Banner + Reworked Zz`Rot Portal
Disclaimer: This is just a suggestion on how banner of command could be brought back and not a hardcore item analysis in which I calculate gold efficiency,etc. (so please go easy on me :D). Also I hope it´s somewhat readable.
Banner of Command https://vignette.wikia.nocookie.net/leagueoflegends/images/9/9e/Banner_of_Command_item.png/revision/latest?cb=20171221055340
Cost: 600 Gold
Active: Unique - Siege: Places a banner at the targeted location. Allied minions in range of the banner gain additional damage against enemy towers and enemy minions (if the enemy minions are in range of their allied tower). Allied minions also gain additional attackspeed, if they are under the enemy tower. (90 second cd which starts after placing the banner)
Noxian War Banner
Cost: 2700 Gold
Stats:
+40 Armor +40 Magic Resist +125% Base Health Regeneration
Passive: For every tower fallen to which Banner of Command "dealt" a certain amount of damage reduces costs of Noxian War Banner by 100 Gold (maximum cost reduction: 300 Gold)
Passive: UNIQUE – POINT RUNNER: Builds up to 20% bonus movement speed over 2 seconds while near turrets, fallen turrets, banners and Void Gates.
Active: Unique - Siege: Places a banner at the targeted location. Allied minions in range of the banner gain additional damage against enemy towers and enemy minions (if the enemy minions are in range of their allied tower). Allied minions also gain additional attackspeed, if they are under the enemy tower. (60 second cd which starts after placing the banner)
Recipe: Banner of Command + 
+ 
+ 750 Gold
Zz`Rot Portal 
Cost: 2300 Gold
+40 Armor +40 Magic Resist +125% Base Health Regeneration
Passive: UNIQUE – POINT RUNNER: Builds up to 20% bonus movement speed over 2 seconds while near turrets, fallen turrets, banners and Void Gates.
Unique Active: Spawns a Void Gate for 60 seconds (60 second cooldown).
Enemy minions trigger the void gate (each wave triggers it only once). If triggered the void gate spawns a group of void spawns consisting of one marker (marks a target minion -> a caster minion, if there are none then a melee minion, if there are none then a siege minion), two hunters (both deal damage to the marked minion) and one devourer (devours the marked minion, if it´s below a certain % of its max hp, and then explodes and deals aoe damage based on the devour damage).
Each void spawn can be killed. Each void spawn also "dies" after doing its task. If the marker dies before marking a minion the other void spawns attack randomly. If a minion isn´t below a certain % of its max hp the devourer does a normal attack.
Recipe: + 
+ 680
