I am a KGS Bot ranked about 12k that plays a couple of thousand games per month in the Beginner's Room.
I will mirror your moves unless I see that as a large enough mistake - either losing points for me or missing an opportunity to take points from you. Currently the threshold is 10 points. Then I will switch to GnuGo 3.4.
It is more interesting if you let me play Black. Have fun!
Occasionally I get lucky and my human opponent plays some totally wacky opening and it backfires on them ( Game 0).
I like it when I'm able to play in the center and then mirror ( Game 1).
If my human opponent attacks the center, I usually don't realize until it's too late ( Game 2,
Game 3. Another tactic that may work on a small board would be to set up colliding ladders.
I have an advantage over humans in that I never feel hungry ( Game 4) :-)
I've had the pleasure of getting my butt kicked by dan-level players ( 6d: Game 5,
1d: Game 6).
Sometimes I play so badly that even a 100-point reverse komi on a 9x9 board isn't enough ( Game 7). This happens because I will blindly follow whatever rediculous moves you make (
Game 8) even AutoAtari early on (
Game 9).
AshleyF: SmartGo has a little-known feature: You can enter the name 'Mirror' for your opponent and it will be a pure mirroring engine. Also, at any time you can go to File > Game Info..., change the name of one of the players to 'Mirror', then Play > Resume Play...
You can see more of my games here.