Pub
Base
Duel
Squad
Weasel (cloaker / x)
Wb
Jav
Spid
Terr
Levi
X
Lanc
Shark
Basing:
When to use:

The weasel (x) isn't used in base games very often. For rare occasions when it is used its to try to break cram by killing the enemy terrier (terr). In the average base game I would not recommend using an x. In most cases an extra spider (spid) or a javelin (jav) would give you better results.

Strategies:

The first thing you have to do is hope that the enemy team did not notice that you are in an x before the game starts. If they know you might as well switch ships. The main goal with x is to surprise the enemy. You may get 1 terr enemy kill (tek) with an x but in most cases probably not. If you choose to use an x wait for the flag room (fr) to calm down a little then make your move. This will decrease your chances of randomly getting hit by a bullet and letting everyone know you are there.

If you are attacking fr use the left and right holes in lower fr to get in. Just like in pub don't touch the flag. Instead go for the enemy terr.

An x is pretty useless defending fr. I would change to a spid, jav, or warbird (wb).