Actually, in Colosseum you get the Pokemon immediately after you snag it. But in a rematch there's no shadow Pokemon.if you fail to beat Damkim, then you'll lose the entei. and if you beat him and get entei then the next time he'll have a sub for entei
I know, I tried cheating the system to get more than one GSC starter. The second guy only had Grimer and Spoink.
Yes, I know I'm late for this.