This material makes a character capable of unrestricted movement below ground or through terrain or other solid barriers, so DMs should take note of that fact. Obstacles and traps reliant on physical boundaries of earth/stone, or the assumption that the character travels across the surface and must climb to access a higher location, may not be significant challenges to a character using this material. Obstacles of these sorts are, however, an excellent tool to highlight the character's advantage. If you are using obstacles of these sorts to restrain the players to the intended play area, it will likely be ineffectual at containing a character of this race. One should be cautious to include challenges which are actually capable of threatening such a character regularly; such as other subterranean/tunneling creatures or constructs; threats which can easily follow them through their tunnels; unseen subterranean dangers, such as underground water, open chasms, or cave-ins due to weak substrate structure; and barriers which are too dense or hard to be dug through; but without punishing the player or coming across as a gimmick. Be careful about who is allowed to use this material, as immature players will likely abuse this to derail the campaign. As should be standard, such players should be dealt with outside-of-game through open communication, but it is often best to avoid the situation in the first place. New players often have difficulties visualizing themselves as another person, let alone another creature capable of moving in ways that they themselves will never experience. As such, if a new player is allowed to use this material, they may need some degree of guidance to remember that their character can tunnel indefinitely without limitations, though it should only take a few sessions to really drive the point home.