In my campaign, one of my players is a hybrid rogue/assassin gnome. (Some of you can see my issue already.) He's level 2 and dishing out 30 damage.
He gets hit and triggers the gnome racial ability
Fade Away. This allows him to become invisible and gain combat advantage. Since he has combat advantage, he can do a rogue
Sneak Attack on his next hit (with the
Backstabber feat adding +2d8). He also uses
Assassin's Shroud as a free action (with the
Lethal Shroud feat adding another +1d8). So he's doing 3d8 after becoming invisible -- that's not even including his attack.
What the hell am I supposed to do about this? I'm making bosses at level 3 that I consider overpowered, and they do overpower the other players in the campaign, but he comes around and does 1/3 the bosses' health in one round if he hits, which he usually seems to.
This is ruining my experience as a DM. I don't want to make every monster too strong, because it's not fair to the other players. Yet if I make anything with a remotely average amount of HP, he kills it in only a few rounds. It would not be fair of me to cater everything to his strength and make the other players suffer. He's a glass cannon, and it's hard to make monsters with high enough hp to withstand his damage and a high enough damage output to take him down without completely overpowering the other players in the campaign.
So what do I do about this? I have monsters and players doing 10-15 damage on average, then he comes along and doubles it almost whenever he wants. How can I bring him down a notch without affecting everyone else?