Player's wishing to have their thieves use thief skills must ask the permission of the Guildmaster to do so. If the Guildmaster refuses permission the opponent cannot play the thief skill card. Permission must be asked for each skill card played.

Even if permission is given the Guildmaster's player may not be targeted by harmful thief skills unless he wishes to be. A non-thief champion able to use thief skill cards does not have to ask the Guildmaster's permission to play them, and that champion may target anyone he chooses.

The Guildmaster is currently the most efficient defense against thief skill cards like Con Game (82/DU) and Hijacking (86/DU). This is still not very efficient, but it is the best defense so far. The high level (ten) and no casting ability keeps this champion out of many decks but the overwhelming power of thief skills is enough to make the Guildmaster a tournament deck regular. Being immune to Fighting Dirty! (3/DU-chase) also makes this card popular with combat decks.

A relatively new theme deck built around permission has shown promise in many tournaments. Midnight, Goddess of Magic (46/3rd), the Arch-Druid (285/4th), Sadira (277/4th), Icon of Magic (19/RR-chase), Nectar of the Gods (20/RR-chase) and the Guildmaster are staples of this theme, designed to deprive opponents of powerful phase 3 support cards. While still a couple cards away from being dominant, this theme may become prevalent in the future.