I watched some Marius games( AI player rated 1123 ) in ChessMaster GrandMaster Editions and he can beat several A.I. players rated 1300-1500.

As I read in other posts, chessmaster AI players cant "detect" their AI opponentes weak points. But, I have more difficulties to beat Marius than to beat 1300-1500 AI players.

Two examples below. In several other tests, Marius won. Probably there is an explanation for this, Im curious.

Watch some Marius matches against higher rated players, he will won most times easily. Thanks for any advices or explanations.

(Sorry for my english, it is not my language.)

Marius(1123-white) 1x0 Eric(1346-black), 15 minutes for each player: 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.a3 Bxc3+ 5.bxc3 Ne4 6.Be3 Qf6 7.Qd3 Nxf2 8.Bxf2 Qf5 9.e4 Qxf2+ 10.Kxf2 Nc6 11.Qg3 O-O 12.Qxc7 Re8 13.d5 exd5 14.exd5 Ne5 15.Re1 Ng4+ 16.Kg3 Ne3 17.Kf3 d6 18.Rxe3 Bg4+ 19.Kf4 g5+ 20.Kxg4 Rxe3 21.Qxd6 Re4+ 22.Kxg5 Rae8 23.Bd3 f6+ 24.Kxf6 Re3 25.Bxh7+ Kxh7 26.Nf3 Kh8 27.Kg6 Kg8 28.Re1 R3e6+ 29.Rxe6 Rf8 30.Qc7 Rf6+ 31.Rxf6 a6 32.Qd8# 1-0

Liz(1488-white) 0x1 Marius(1123-black), 15 minutes for each player: 1.c4 Nf6 2.Nc3 c5 3.g3 g6 4.Bg2 Ng4 5.e3 d6 6.Nd5 e6 7.Qxg4 exd5 8.Qd1 Nc6 9.Bxd5 Nb4 10.Qb3 Bf5 11.Bxb7 Nc2+ 12.Ke2 Rb8 13.Qa4+ Ke7 14.g4 Bxg4+ 15.Bf3 Nxa1 16.Bxg4 Qc7 17.Nh3 Rb4 18.Qa6 Bh6 19.b3 Nc2 20.Bb2 Rd8 21.f4 f5 22.Bf3 Rdb8 23.Kf2 R8b6 24.Qa5 Kd7 25.Bd5 Rb8 26.Be6+ Kc6 27.Qxc7+ Kxc7 28.Bc3 R4b6 29.Ba5 Re8 30.Bf7 Re7 31.Bg8 Kb8 32.Bd5 Ra6 33.b4 cxb4 34.Bd8 Re8 35.Rb1 Rxd8 36.a4 Rxa4 37.Rb2 Bg7 38.Rb1 Ra1 39.Rb3 Bf6 40.Ng1 h6 41.Nf3 Kc7 42.Bf7 a5 43.Bxg6 a4 44.Rd3 b3 45.Rd5 b2 46.Rb5 Rb8 47.Bxf5 Rxb5 48.Bxc2 Rc5 49.Nd4 Bxd4 50.exd4 Rxc4 51.Bh7 a3 52.Bg6 Rd1 53.Kf3 a2 54.Bd3 b1=Q 55.Bxc4 Qf5 56.Be2 Qh3+ 57.Ke4 Re1 58.Kd5
Qb3+ 59.Ke4 Rxe2+ 60.Kf5 Qe6# 0-1

Engines at default settings.
PC: Intel Core 2 Duo T5800, 3GB DDR-3 Memory

Seconded.

The issue of under and overrated players has been discussed on this forum before, and it seems that personalities that some describe as easy others will describe as hard.

But Marius definitely sticks out as an overrated player.

His endgame is particularly sharp. I have to have a big material or positional advantage in the endgame to take him down. And even then, if I make a slip up, he'll pounce on it.

His mating combinations are impressive, but unrealistic for a 1127 player playing 10-minute games.

I've been playing the computer personalities against each other to get a better feel for which ones are stronger. Marius beat everyone up to Orin, who won (0-19-1). A couple of the lower rated players hung in there (Marius beat Krycek 10-8-2, beat Willow 13-7-0, the rest were larger margins of victory). I play them in G20 matches.

The comment about impressive mating combinations is a good one. You can use the Pandolfini ratings diagnostics on the computer personalities. Even very low rated players can crush the Checkmate part of the exam. I don't remember the details, but I'm sure Marius got all of the mating combinations in the exam. And naturally he can see mate-in-8 in a couple of seconds!

I haven't tried the other portions of the diagnostic exams, but I'll try to get to that some day. Naturally those tests, and particularly the mating tests, play to the computer's strength.

Thanks for the answers, my question is solved.