Here are my suggestions for a rogue character in KotC:
Special abilities:
"Spells": Controlling attribute is DEX. Either make this like the other spell systems or give them new and stronger "spells" automatically at level up.
There would be two categories/types of "spells": traps and alchemy (alchemy = bombs and enchanting weapons). All "spells" would cost gold when "casting".
Traps would always be only one field large (maybe larger at high level). I'm not sure if they should be visible or invisible. If an enemy walks on that field, the trap triggers. If an enemy rogue walks on that field, the trap is automatically disarmed. And they would be destroyed by damage spells (or maybe only specific spells like fire spells?).
Of course this would only be in battle. After the battle all traps would be disarmed.
If I may say so myself, this would imo be the only working (and fun) trap system in any RPG ever.

Bombs and enchanting weapons would work just like in other RPGs...
Use magic device: Just like in D&D, but only based on character level and intelligence (since there are no skills).
Insightful strike: Just like the Swashbuckler feat from D&D/NWN2: Instead of STR bonus, INT bonus is added to damage rolls, but only when using light weapons or a rapier.
If it's difficult to implement sneak attacks, they could get better critical hits instead...