TL;DR: the short version:

TL;DR: the short version:

What is Chaos-Tower?

Chaos-Tower is a casual out-of-the-box format best for 4 players.

It's a single 400 cards, five-color deck shared by all the players.

And there are some legacy elements.

How to build the Chaos-Tower/What do you need?

Build a singleton 400 cards deck.

There should be around 140 lands in there.

Feel free to use any cards you want to, but I recommend reading through the blog, there are some ideas for construction.

Optional: 

Have some unopened packs with you. 

You should need like 2-4 packs per game played, some inner-sleeves and a marker.

If you don't want to spend that money or have no packs with you, there should be a sideboard (maybe made out of random bulk).

How to play Chaos-Tower?/The rules.

Rule 1: 

There is only one deck and one graveyard. 

Cards referring to "your" deck or "your" graveyard now refer to "the" deck or "the" graveyard.

Rule 2:

There is one free mulligan.

If your second hand contains less than 3 lands, you can reveal your hand and mulligan again.

Repeat this process if necessary.

Rule 3:

After all Mulligan resolve, the deck gets separated in 4 (more or less) equally sized piles.

One of those piles is chosen to be the "active" deck.

The other three piles are called the "passive" decks.

Passive decks are marked with tokens/coins/dices on their top.

Each player is only allowed to draw from and to search the active deck.

After a pile is completely drawn or a player searched the current active deck, one of the passive decks is chosen as the new active deck. 

The former active deck (if still existing) gets marked as a passive deck.

Rule 4:

Starting life total is 30.

This might be lowered soon, because games tend to be 3+ hours.

Rule 5 - the Legacy-Rule:

New cards can be added to the deck by playing one of the 5 wish-cards.

All wishes have only the following effect:

• "Choose a card you own from outside the game, reveal it and put it into your hand. 
  Exile [cardname]."
• When a card is selected, choose a card from the graveyard, from exile or from your hand with the same color and remove it permanently from the game. If the selected card is multicolored, the card to be removed also has to be multicolored. Cards that are colorless, artifacts and cards with Devoid also share one category.
• The newly added card has to be signed by the player of the wish (maybe sign on an inner-sleeve?).

Cards "you own from outside the game" refer to cards from a prebuilt sideboard or from a (randomly selected) booster pack (recommended).

The sideboard should be around 90 cards (6 packs) and either be made of random bulk or build in a way to have all colors and mechanics like removal, ramp or counter magic represented equally.

The sideboard should then be separated into 15-card packs (just like cube-draft).

Then there is only one pack opened by the active player.

Rule 6:

Normal Magic: The Gathering-rules apply.

I wanna thank my friends Kai and Vik for playtesting with me and for figuring out some additional rules.