Maybe all the players could warp to the dimension (kind of like a shared dream, allowing the players to stay together for the boss fight), and when that happens, the Clever player has it's stats increased proportionally. 

In addition, he can spawn Cybermen when there are more than one player, rather than just Cybermites.

Maybe he/she could also have a few new attacks and behaviors as well when fighting multiple players, for example, Teleportation (a bit odd, but seeing as the battle is in the head, I think it could make sense).

Also, as long as there's at least one player still alive and fighting, there can be an entity  which resembles the Clever Player of the Player that the Cybermites were thrown on. This Clever Player will be running back and forth in place or side to side in the spot the players got teleported from (unless there is a nearby drop), and may every now and then let off some attack, but is mostly, overall, not that harmless.

Right-Clicking on the Special Entity will teleport a player to the boss area where the others are fighting the actual boss in the mind.

 Yes thats a great idea

1.normal cyber-man

.shoots laser blasts from gun located on the arm

.partly upgrades a villager (into a cyber villager. the cyber villager only wears a cyber man helmet, he also just does melee damage and can't upgrade other villagers)

2.classic cyber man

.only does melee damage

.quicker than other cyber men

. explode on death

3.tenth planet cyber man

.neutral mob (only attacks you if you attack them)

.does melee damage but has a higher strength value (there melee hits are stronger than any other melee attack in the game)

4. wooden cyber man

.shoot fire balls (like the ones fired by ghast) they cause an explosion of fire that does some physical damage but mainly it is just fire that carries on spreading

.when you are close to them they do melee damage which on every hit the mob is set on fire as well

5. cyber leader

.spawns other cyber men (random versions of them)

.fully upgrades villager (so they turn completely in to a cyber man)

.shoots lightning projectiles (to simulate the electric touch)

6. 2005 cyber men

   .has a gun that shoots normal lasers

   .has electric touch

   .can upgrade villagers into cyber villagers

   .these will spawn closer to villages

   .when you kill the cyber leader, if one of these are near by they will turn into a new cyber leader and it's texture/skin will also change to suit the cyber leader's armour.

when you use the screw driver on them or the sonic shades they freeze for round about 5 seconds since they are technology and the screw driver can manipulate technology.

when killed there is a random chance they drop their head, when put into a crafting table surrounded by iron and in the centre top piece a redstone block it creates another cyber head but re-named handles.

cyber mat:

when mining any block there is a chance it will spawn an ender mat, this will do damage to you (melee) and when it spawns from the broken block it summons cyber men to your current location

cyber mats can also be obtained by:

crafted- 1 glowstone dust in the middle of the crafting table surrounded by steel and can be tamed with the right click of a sonic screw driver and when tamed it can

.down grade a cyber villager back into a normal villager

.will locate other players and mobs for you

.if you or your cyber mat is attacking you it will spawn two cyber men that will not harm either of you but just the attackers and they will then de-spawn afterwards

how else can they be obtained part 2:

spawn when cyber man is killed- chance is 1 in 3

spawn at night- chances of them spawning is 1 in 5

New audio and quotes for the cyber men:

.delete

.You will be upgraded

.alert alert 

.all hail the cyber leader 

.destroy the daleks 

.emergency, malfunction

new planet and how cyber men spawn:

there should be a new planet available to travel to in the TARDIS called Mondas (in the DW universe this is earth's twin planet, and where the cyber men first ever came from)

here are some of the new planet features Mondas should have:

.is a rocky and icy abandoned waste land

.always night

.1 in 2 chances of it snowing but it is heavier than normal snow

.only the cyber men spawn here (when I say the cyber men I mean just the tenth planet cyber men and the classic cyber men)

.lots of caves

how else should they spawn on the over world:

.random generate at night

.random chances that a meteor comes down from the sky and in it is a small square structure made from steel and inside are three cyber men spawners that spawn the cyber men and that they start a small invasion. when the meteor comes down from above it shouldn't just land, it should create a small explosion of which the meteor with the little spaceship/steel structure burry themselves into the ground/hole. also ores and other minerals should be found in the meteor.

The wooden cyber man does not say delete he says incinerate. [this only applies if you add the wooden cybermen, and when trenzalore is re-added this is where they should spawn]

Well, I'll start adding some of these.

A few, I'm not really sure about though. Classic Cybermen Exploding on death or only dealing melee damage for instance (tbh, neither are really that accurate as they did use Cyberguns or some variant of  hand arc frequently, and they never really did any damaging explosions on death. They did do melee sometimes, but it wasn't actually their one and only form of attack.).

As for Mondas, I have a thread on it= https://swdteam.com/forum?p=thread&tid=218

Unless this hasn't been suggested, I believe that when cybermen (preferably classic cybermen) walk over gold blocks they should take some slight damage.

 I've seen it somewhere, though I'm not sure who it was. I'll add this to the thread.

 Added it to my general changes thread (link)

I don't know if this has already been suggested but maybe the Mondasian Cybermen could be added (maybe even the planet)

 I have a thread here if you have any ideas for them: Mondas/Marinus and Time Zones

UPDATE: Added more information after watching Silver Nemesis. Mainly golden tipped arrows, golden coins, and the headsets used to initiate a partial conversion

Hey Arc did you add everything to do with  //schematic you said you would plz could you I would really appreciate it!! ~Cyber City Vice Mayor~

Yep.  I added a link to the world edit wiki.

I love these ideas, especially the classic Cyber controller! I'll talk to John about it as soon as we're discussing ideas again.

 What are you doing here man? go back to making the video for update 43! I'm just kidding man its fine i know that making and editing a video is hardwork, well not that i speak from experience but regardless i still know that its hard. Keep doing your best man!

 Perhaps golden coins will be a currency in a new world "Medival England" I shall add this to my earth timezones thread I am working on, shall I reference this thread? I think so

 Sure. If you use the idea, just let me know. I'll include a reference in my thread about yours