Assassins are the most expensive unit in Stronghold 2, surpassing even the knight in honor cost. They are a strictly specialist unit who is very frail and cannot stand up against armoured units. The assassin's utility however, greatly justifies his price tag.
Compared to other games, the assassin's traits are greatly bolstered due to his high cost: he moves at a very high speed comparable to cavalry, and he can almost instantly scale any wall. The stealth ability of the assassin breaks only at the very close proximity of units (a few tiles) and there is no blur at medium range, making the assassin a very deadly commando.