I don't think up good names, so I'm counting on the rest of you.

Modes:
-A mode in which each non-IT has 3 lives. Works similar to Sudden Death except the first 2 tags are freezes and the last is defeat.

-A mode in which having people frozen cause the IT's point value to go up. Say the IT gets 1 point for each second a person is frozen, if 5 people were frozen, he'd get 5 points every second. The points keep accumulating until either time runs out or a certain number is reached. Depending on the number of players, the score needed for the IT to win would fluctuate.

-A mode in which being IT is like a short-term disease. Every person who gets tagged becomes IT, but being IT only lasts for a short period of time(maybe 5-10 seconds?). The first IT's infected time would be around 15 or 20 seconds. The goal is to have everyone IT, or have no one IT. If the game ends with no one IT, the game say that the last person infected (and possibly the initial IT) lose. If everyone gets infected, the initial IT wins.

-Team Fire Fight: I already have a name for this one. It's exactly the way it sounds. Players in the game are split evenly into 2 teams at random (and either given appropriately colored icons or some kind of overlay) and the game is played out like a normal fire fight round, except teammates can't hurt each other.

-How about a race mode in which players have to dash from one randomly spawning checkpoint to another? First person to 10 points wins.

Items: (most of these have names)
Bomb- Can't be picked up. Freezes everything in a 3 space radius from it. Immobilizes ITs for 5 seconds.

1-UP- Survive one encounter with an IT. (2 second recovery time after being tagged before you can be frozen again)

Mirror- Spawn a look-a-like of your character that does everything your character does but backwards. (You go left, it goes right. You move up, it goes down) When tagged by an IT, it disappears. It goes away regardless after a while.

Invisibility- Makes your character much harder to see. (Thanks to the magic of BYOND4.0, this shouldn't be that hard) Wears off.

Confusion- 3-time use item. Fires like a fireball. Whoever it hits has their movement controls reversed for 10 seconds.

Slow down- Makes all your opponents slower for 10 seconds.

General gameplay:
-Put a time buffer between when you get unfrozen and when you can be re-frozen. I've seen too many people spamming freezes and unfreezes.

-Make it so Goombas can't freeze ITs. I don't know if it's a bug or not, but they definitely shouldn't be able to do it.

-Make Fire Fight not random. Geez.

-Vote mute. Players vote on whether or not to mute someone. 2/3 vote or higher to succeed.

-Vote boot. Players vote whether or not to boot someone. 2/3 vote or higher.

-Vote ban. Players vote on whether or not to ban someone. 4/5 vote or higher. Ban lasts for an hour.

-Vote re-host. Players vote on depriving someone hosting ability. 3/5 vote or higher.

Most of my suggestions are malleable, so feel free to change things the way you see fit.
Also, I feel like I owe you guys these suggestions anyways, so no thanks necessary. (Of course these suggestions are probably so horrid I wouldn't have earned one anyways.)
My apologies if any of these have already been submitted.

Q:-A mode in which each non-IT has 3 lives. Works similar to Sudden Death except the first 2 tags are freezes and the last is defeat.
A: Nah Sorry the IT would of course... be the runner while the players are the IT.
I don't understand what you mean. There would be 1 IT, who tags the however many non-ITs(who can be tagged 3 times and then be defeated.) It's just like Sudden Death except with lives, like stock in Super Smash Bros.

Q: -A mode in which having people frozen cause the IT's point value to go up. Say the IT gets 1 point for each second a person is frozen, if 5 people were frozen, he'd get 5 points every second. The points keep accumulating until either time runs out or a certain number is reached. Depending on the number of players, the score needed for the IT to win would fluctuate.
A:This is a good idea, but needs a bit more thought into it. A few minor flaws like how much points to win, and with all the non-its the IT will of course win real quick.
These are all very rough ideas, so further suggestion is appreciated.

Q: Bomb- Can't be picked up. Freezes everything in a 3 space radius from it. Immobilizes ITs for 5 seconds.
A: How about instead of freezing it just kills you and you don't spawn back for another 15 seconds, if it's the IT then he will be frozen 5 seconds.
That makes more sense realistically, so meh.

Q: Mirror- Spawn a look-a-like of your character that does everything your character does but backwards. (You go left, it goes right. You move up, it goes down) When tagged by an IT, it disappears. It goes away regardless after a while.
A: Seems a bit complicated, but if Kirby wants too work on it, it'll work. Also Doppleganger seems like a better name for it.
I like the name.

Q: Confusion- 3-time use item. Fires like a fireball. Whoever it hits has their movement controls reversed for 10 seconds.
A: Needs more thought into it, like what the item is.
Agreed.

Q:-Put a time buffer between when you get unfrozen and when you can be re-frozen. I've seen too many people spamming freezes and unfreezes.
A: Would lose the point in the game and would add more unfreezing/freezing if they were unfrozen when noone unfreezes them.
I don't mean that the just thaw out over time, I'm suggesting that once a person gets unfrozen by another player, they can't be refrozen(by an IT or goomba, etc) for a short period of time, so the non-IT can escape. Basically so we don't see this with rapid succession all the time:
PlayerA has been frozen by a Goomba!
PlayerA has been unfrozen by PlayerB!
PlayerA has been frozen by a Goomba!
PlayerA has been unfrozen by PlayerB!
PlayerA has been frozen by a Goomba!
PlayerA has been unfrozen by PlayerB!

Q:-Make Fire Fight not random. Geez.
A: GM's and Admins have a magical button called "Fire Fight" So not random.
I thought that Fire Fight occurred randomly 1 in 10 times someone chooses to begin a round. Correct me if I'm wrong.