Sandbox Party/Host Ideas
There can be a party link which you can get by clicking on the Copy Party Link button (as usual), or the person who first joins can 'host' the server.
"P" is used to publish the server. A small host link appears on the top right. Upon hitting P, a GUI (Guided User Interface) will pop up.
Enabling/Disabling certain tanks
Arena Closers, Motherships, and the three types of Dominators have checkboxes under a category that says "Special tanks" next to them that will enable them to normal people. Also, although it probably won't be used/necessary (except in games), you can disable tanks in general (lvl 15, 30, and 45 tanks). You can also disable the actual starting tank, but a new one to spawn in will be necessary (for instance, you could have a Hide 'n' Seek server in which you spawn as a stalker or a landmine, but can become a dominator if you are the seeker). Unchecking them prevents players from being that tank. For instance, unchecking Arena Closer will make the Arena Closer unavailable by pressing \. Upon getting where the Arena Closer would be in \ (after the Necromancer), you would get a notification at the top (where it says Arena Closed: No players can join, The NW dominator is now being controlled by BLUE, etc.) saying "Arena Closer has been disabled by the host." You can also enable/disable the ability to become boss tanks, and a certain tank's full level (for special tanks, such as the Arena Closer, Mothership, Dominator, etc.)
Toggling controls in general
The host can also enable/disable certain controls, such as K to level up, and O to suicide. God mode can also be enabled/disabled (and locked). PvP can also be disabled (it prevents a tank's bullet/drone/trap from harming another tank, not making it invincible). You can get a couple buttons to place Dominators, and they can be A) Force AI (No one can control), B) Host Chooses (so the host can decide who can play), and C) Regular. You can also change teams. Available teams are: FFA/None, Blue, Red, Green, Purple, Yellow, and Gray/Grey. You could become 'full size' tanks, like a lvl. 140 Mothership, a real Arena Closer, or a real Dominator. You could max out skill points, so you could have 7/7/7/7/7/7/7/7 (Normal tanks), 10/10/10/10 (Smasher), or 10/10/10/10/10/10/10/10 (Auto Smasher).
Giving people special features
For certain mini-games, or if you are playing FFA with friends, you can have a 2-8 digit "host code" that if another player presses "P", they can enter it, along with seeing the customary features (e.g. there'd be the gamemode, a list of disabled tanks, etc.) If you enable it, you can set your code, so that in FFA, you can give some people the ability to 'team' up with you (e.g. if you were playing a game and you were arena closers in case somebody broke the rule(s), you could use it to enable invincibility [and PvP] to kill the rule breaker). Or, you could enable teaming for your friends so that you could play together on Sandbox, while other people can join as FFA. You could also be full-size Arena Closers.
More party/server features
When you join a party, rather than (for example) diep.io/#544A0D1DBB30842F500A26, you would have a 'smart' link, such as diep.io/#5000013E3DAAB1
3E=Link verification code (so no one can just get in a certain server)
3DA = Green team + Verification (no instant team switching!)
AB = Party verification
(Opt) 1 = Party #
Broken down: diep.io/#5 00001 3E 3DA AB 1
Teams: 0 = FFA/No team 1 = Blue 2 = Red 3 = Green 4 = Purple 5 = Yellow (Polygons/Polygon based bosses/Arena Closers) 6 = Gray (Fallen Bosses)