Mutator ReadMe
Some general guidelines

Installing the UMOD

In a perfect world, anyone double-clicking the UMOD file would be guided through the installation process. Unfortunately, it's not a perfect world and some seem to encounter problems at this stage. If the UMOD file extension is unassociated, you should associate it with:

<path to your Unreal Tournament folder>\System\Setup.exe install "%1"

Now, try double-clicking the file again - hopefully, it'll work now.

What's a Mutator?

A mutator modifies the standard game play in various ways. It is not as powerful as a true mod, yet can handle stuff such as tweaking the default properties of classes (for instance, turn all the lights in a level blue), modify the players a bit, replace items on the level and so forth. Any mutator should be compatible with any game type, so that you could for instance use "MyMutator" in combination with the Assault game type.

However, combining several mutators might cause them to conflict with each other. For instance, one might want to reduce the movement speed of players, while another tries to increase it. There are other, more subtle situations as well - consider combining two official mutators, the "Rocket Arena" and "Instant Rockets". Now, when you do this, you might end up with standard Rocket Launchers, rather than Instant ones. The reason for this is that "Instant Rockets" tries to modify existing Rocket Launchers so that they can't load up multiple rockets, while Rocket Arena replaces all guns on a level with Rocket Launchers. Depending on in which order these two mutators appear in your Mutator list, things might get messed up. Put simply, "Rocket Arena" won't allow any other mutator to mess with the Rocket Launchers, so if "Instant Rockets" appear below "Rocket Arena" in the Mutator list, you won't get the Instant Rocket Arena combo you were looking for. In this case, rearranging the order in the list will solve the problems.
This is just one example of how different combinations of mutators can yield unexpected results - it might be a good idea to try to keep this in mind while you're playing around with various mutator combinations.

One could say that there are two basic types of mutators - client-sided mutes and server-sided ones. Client-side mutators requires that the client (the machine joining a game) has the mutator installed. If not, it will generally be downloaded to the client. Such mutators will usually have features not possible to code when dealing with server-side mutators (e.g. custom graphics and sounds, custom items and so on). Server-side mutators are somewhat more limited, but you can join any server using these mutators without having to download a single byte. Whee!

Using the Mutator

When you've installed the mutator, launch Unreal Tournament. When starting a new match, click on the Mutators button and browse through the list. If everything went well, the new mutator should show up somewhere in the list. Double-click on the mutator, or drag it to the right-hand box to include it in the match.

Some mutators are configurable - if so, they should show up in the "Mods" menu item in the Menu bar (this item is invisible by default and will only show up if you've got a mutator or mod installed that makes use of it)

Cheers!
Bane