Make sure you have Okaluk and Rakash, get the skill "taunt", and also have one other hero with Leadership.
With the stealth ability, O & R can avoid an additional 1/3 of all attacks. Adding taunt, the OL is forced to attack them (unless legally cannot target them), then to top it off, have the other hero place a dodge order on them (or they could place it themselves using a ready action).
I just conceded (after only one dungeon) when at the start of level 3, the injured heros simply kept restocking for hit points (they were very close to death in level 2), as my copper beastman war party was simply unable to get through the stealth, and subsequent dodge rolls. When one considers the attack die, with only a single X, but the stealth die with two "x's", using a dodge order along with that is exceptionally difficult. I have read different opinions on the math of such possibilities, so give it the 67% that seems to be predominant. Though it would seem that this lessens when being forced to roll a 2nd time (dodge), it instead increases by having to risk the 16 and 26 "x" results on both rolls.
Result: Game over, the OL cannot win if this comes up early in the AdvCamp.
There are those that will point out that with TOI, the OL has monsters with the stealth ability, but they only come around on occasion, as opposed to the full-time play of a member of the hero party.
Though I am fairly new to Descent, I am an experienced board gamer, and it seems to me as if this combination of heros might not have been fully thought out. Still, I defy any OL to allow the heroes to create this party (customized) at campaign start, and see if this OL can even last through copper levels.
For my play, we are looking into a house rule to change the design effects of stealth, else we are losing willing players. Eitehr we play without TOI as a whole, or create a new mod that would address this overbalance. Until FFG recognizes that this combination is death for the OL, though I recommend Descent as a game, I cannot recommend TOI as an expansion.