Give the right build, Cascade of Blades is way too powerful. This is from the WotC Character Opts board...
A level 30 rogue/ranger/Shadow Assassin/Deadly Trickster can, in fact, brutally murder Orcus all by himself in just one round. And he can do it flawlessly too, because if he doesn't win initiative naturally, he can use his daily Trickster's Disposition to make Orcus' initiative roll a natural 1. I'll repost the statistics over here for convenience:
Imperiling Strike Attack Bonus
+15 half level
+8 Dexterity bonus
+6 Duelist's dagger
+1 Rogue Proficiency
+1 Nimble Blade
+3 proficiency bonus
+2 combat advantage (First Strike, Duelist's dagger, flanking, etc.)
+4 Shadow Assassin
TOTAL: +40 (against 51 Fortitude defense)
Blade Cascade Attack Bonus
+15 half level
+7 Strength bonus
+6 Duelist's dagger
+1 Rogue Proficiency
+1 Nimble Blade
+3 proficiency bonus
+2 combat advantage (First Strike, Duelist's dagger, flanking, etc.)
+4 Shadow Assassin
+7 Imperiling Strike
TOTAL: +46
Non-Critical Damage
2d4 with Gauntlets of Destruction: 6 average damage
+8 Strength modifier
+6 Duelist's silver dagger
+10 Belt of Titan Strength
+3 Weapon Focus
+2 Light Blade Precision
(+1 Two-Weapon Fighting) for main hand
TOTAL: 36 on main hand dagger, 35 on off-hand dagger
Final Statistics
Chances of landing crit on hit with Light Blade Mastery: 2/19
Total average damage of main hand including crits: 40
Total average damage of off-hand including crits: 39
Total average damage of both hands: 39.5
Number of hits required to deal 763 damage to bring Orcus to bloodied, from 1525 hp to 762 hp: 19.32
Number of hits required to deal 1535 damage to bring Orcus to dead, from 1525 hp to -10 hp: 38.86
Number of rerolls available: 4
THE MATH:
Assuming a maxed +46 attack bonus (after Imperiling Strike), we have a Blade Cascade chain with an average number of hits equal to 19 times the number of rerolls plus one (if somebody bothers to do the math and finds it's wrong, please tell me so and why.) Now, Imperiling Strike, with a +40 attack bonus, has a 50% chance of hitting with a regular attack, so half of the time we will start our Blade Cascade with less than four rerolls. In particular, we should note that our racial reroll has a +2 bonifier, so that's the one we'll use first, since any extra bonifiers on the Cascade are wasted.
Considering all this, we have a 50% chance of having 4 rerolls when starting Blade Cascade, 30% of 3 rerolls, 10% of 2 rerolls, 5% with one, 2.5% with none, and a 2.5% of losing all rerolls and failing to land Imperiling Strike (this, as you already know, means you are already dead). The average damage values of each are 3752.5 (4 rerolls), 3002 (3 rerolls), 2251.5 (2 rerolls), 1501 (1 reroll), 750.5 (no rerolls) and 59.25 with no IS.
With 39.5 average weapon damage, this gives a final average damage of 3097.29 hit points, enough to kill Orcus twice. To that we could add an average 33 damage from Imperiling Strike and a maxed 6d8 from a critical sneak attack done when Orcus is bloodied. If we added Raise the Stakes, these numbers would improve a bit, but the point is already made.