After playing a bunch of quests and reading the others the base game quests put a high importance in mobility Grisban seems extremely underpowered. With 1 awareness he is always the target of tripwires, negating his movement, which he only has 3 to start with. His heroic ability will only ever trigger with disease, as immobilize will go straight away perform the ability triggers, stun is removed as an action, and poison is a strength roll to resist which he has 5. Disease doesn't even do much as his willpower is 3. The heroic feat is nice I will admit but does not negate the extreme downsides. If there was a quest where you only had to kill all the monsters and there was no time limit then he might be able to achieve something but I have not come across a quest like that so far.
Very interested to hear any thoughts on any point raised.
As others have pointed out, Grisban is likely to be resting every round and using fatigue to move.
His heroic ability works against immobilised, as that normally lasts until the end of the turn. In fact, in some scenarios, I have found him more mobile as a result (against Meriods and the like). He's the only hero who can move 7 squares on the turn he starts immobilised.
It's a good fall back for poison and disease too.
That doesn't work. Grisban's heroic ability specifically says he removes the condition when he recovers fatigue from performing a rest action. When taking a rest action fatigue is recovered at the end of the turn so he can't remove immobilize until it would have went away naturally ie at the end of the turn. He already has a 91% chance to discard poison so a minor boost at best. Disease is the only condition his heroic ability works on and disease is pretty rare. His heroic ability is bad to the point I would recommend house ruling it to he removes the condition on resting rather then on recovering fatigue to make it of at least occasional use.
Yes he can use fatigue to move but so can every other hero so they have much greater flexibility. Using fatigue move allows him to break even at a distance of 4 hexes to a move 4 hero. Anything greater then 4 and he is still at a disadvantage (costs 1 more fatigue from 5-7, 2 more fatigue at 8-10 and he can't go beyond 10) and of course this is assuming he never spends fatigue on skills.
He is flat out the worst hero. That said he isn't so bad taking him is going to doom you. The variance in dice rolls makes a much larger difference then him lagging behind a bit.