My friends and I are starting a MERP campaign and only I have experience with MERP. One of my friends wanted to be a shape-changer, but my Second Edition MERP book does not cover how to use Martial Arts, Adrenal Defense, or Shape Change, so I am at a complete loss.
These skills are address in the Second edition rule book.
On page 218, under section A-6.2 Martial Arts and Adrenal Defense
Adrenal Defense says:
If a character is not using Armor or a shield and he moves at least 5 feet during a round, his skill bonus for Adrenal Defense is added to his normal DB. This applies to each melee, missile, and directed spell attack which he is aware of (i.e., it does apply to an attack that surprises him)... there is no stat bonus for this skill.
The Martial Arts skill is listed on the same page in the same section and I have posted it here:
There is a new optional profession that is called Shape Changing, it is designed specifically for this type of character. It can be found on page 217, and reads as follows:
The cost of being a Shape Changer is pretty high, but there they are, such as it is.
So in summary:
Adrenal Defense is a bonus DB to add to their character normal base DB, but only if the character can see the attack coming, but it can be pretty high making the character very hard to hit.
The Martial arts skill is a little complicated and hard to advance because there are two distinct paths, one striking and one sweeps, and the Novice level has a pretty low attack maximum but it must be advanced through development points before you can increase the Standard Level, and BOTH must have higher or equal number of ranks before you can advanced Expert.
The Shape Changer as the complicated formula on how you can voluntarily shape change, and although you get a bonus to this each level, this is countered by the fact you only get 14 development points (rather than the normal 15). You can also have circumstance where you are forced to change (you get angry, or take a hit, or fall).
The skills you've mentioned are all in Rolemaster (in its various versions), which is what MERP is based on.
Option 1: So the (not easiest) way to do this would be to run Rolemaster instead of MERP (they're compatible, but Rolemaster is like a 6-volume encyclopedia to a single-volume dictionary of MERP!) - This is what I did for my MERP campaign. It has all these skills as well as a much larger set of options (how much money do you have?) and characters and so on; if you choose this option, ask for more details!
Option 2: Somewhat less effort!. Create a custom race for the Beorning, base in on "Men" and then add some special skills for them to use in the new categories.
The three skills translated from Rolemaster to MERP are:
Adrenal Defense: Special Skill. No bonus except for rank. Each rank gives a direct bonus to DB if the character is aware of the attack. First ten ranks give +5 each, next ten give +2 each etc. Miscellaneous Skill.
Martial Arts: Combat Skill, Strength adds, use tooth and claw when in bear form, use grappling and unbalancing otherwise. Frankly this skill should be there for any character anyway to allow fisticuffs!
Shape Change (Control Lycanthropy in Rolemaster) Taken from RMC2; use the table on MT-2 (p 77 to resolve) use the "General" column to determine if the change is successful, then adjust modifiers as you feel; -30 for daylight, +20 for full moon, etc. This skill is based on Constitution and Self Discipline in Rolemaster, so for MERP, Constitution is a good fit to add to it.