Certain rule variants do not fit into an existing category, or they are too short to merit their own. These are listed below:
Armour, Magic
At the DM's option, magic armour, in addition to its protective bonuses, may also impose a weight reduction. For every "plus" of the armour, lower the armour's ENC value by 10%. For example, a shield +1 would be 10% lighter than a normal shield (100cn) for a total of 90cn. A suit of chain mail +3 would be 30% lighter than a normal suit of chain mail (400cn) for a total of 280cn. Note that the standard restriction on magical "plusses" is +5, so no enchanted armour can weigh less than 50% of its normal counterpart. To be consistent, it is recommended that cursed armour imposes an encumbrance increase of +10% for every -1 penalty (i.e., a shield -1 would weigh 110cn).
Energy Drain
In the official rules, energy drain attacks reduce the victim's experience level (RC/154); while terrible in effect, this can bog down play as the target re-calculates hit points, THMod, total spell level, etc. To streamline play, energy drain attacks on Trid permanently reduce the victim's CON score by 1 for each level described in the RC. For example, a wight's touch reduces CON by 1; a vampire's energy drain reduces CON by 2.
Range, Point Blank
In addition to the standard short, medium, and long range, missile weapons can fire at point blank range. This range is equal to half the normal short range and grants a +1 THMod (short range = +0 THMod, medium range = -1 THMod, long range = -3 THMod). When determining point blank range, round fractions down. For example, a long bow (range 7/14/21) has a point blank range of 3 [7 / 2 = 3.5 = 3].