TL;DR: The customized single-player match is actually in the two-player menu:
There are four commands in the main menu:
- Go to the single player menu
- Create a single or multi-player game (this is the one you want)
- Play over a local area network or the Internet
- Go to the options menu
The picture with one worm is for a "quick game" (no custom maps or crate settings) and missions
The picture with two worms is also for a single player game against the computer + custom options
Yes, there are only four options, but this still gets me every time: I always click the one worm, thinking that is for all types of single-player games, and then wander around inside that menu endlessly.
Create a single or multi-player game
This allows for the following custom options:
Under "Scheme options", there are two large picture buttons:
- Set or view the weapon options (adjust Ammo, Delay, Power, Crates)
- Set or view the game options (adjust additional create and time options, including time between players in a "hot-seat" game)
When choosing teams, you can choose multiple human and computer teams. If you choose multiple human teams, this will start a "hot-seat" game with friends. Otherwise, you are simply creating a single player game against the computer.