Common MMO Mechanics for BTD Battles

This page is for suggesting Ninja Kiwi to put some common MMO mechanics in the final release of BTD Battles or BTD Battles 2. As the mechanics stated here are common and not original, I don't want to make many different pages.

Chat
Every multiplayer game needs in-game chat. Text chat is enough, however Ninja Wiki can put voice chat or video chat in if they have the money.

Friends
Every multiplayer game needs a mechanic where you can invite a specific user to fight you, and also a friend list where you can send messages to such users and do Informal Tradings as explained below.

Group Battles
There should be a mode where multiple players are divided into two teams and battle in the same track at the same time. Each user has his/her individual timely income and towers, but they share the same battlefield so every towers employed by the users of the same team will be on the same screen and technically the same "army". Also, all bloons that are employed by users of the same team will appear on the opponent's screen together.

Group Missions
Proper multiplayer games aren't just about PvP. There should also be some Special Missions where you can invite your friends and do the Mission together using the shared battlefield mechanic used in the Group Battles.

Inventory & Informal Tradings (also expand as a catalyst to bring back Items and Special Agents)
Remember the Crafted, Loot and Equip Items? Well, sometimes there're some special, rare items, special agents and limited towers that some users have but other users don't. There should be an "Inventory" for items/towers/agents of such categories to be stored so the owner can use them in whatever match they need in their playing time. Thus, there should also be a system where users can make deals and trade those items/towers/agents for medallions or other items/towers/agents. The "price" of the items/towers/agents will be discussed and decided informally between the two users, and the seller may accept or decline the deal with the buyer at will.