Editing MTH:Weaknesses (section)

==DECREASED DAMAGE==
The wounds dealt by this power are not as grievous as they could be.  This weakness may only be given to powers that deal lethal or aggravated damage.  If the power previously dealt aggravated damage, it now deals lethal; if the power previously dealt lethal damage, it now deals bashing.

Note: Since bashing damage to a character that is incapacitated spills over into lethal, this is still worth a Class decrease if used on a power that normally does lethal.  If the player truly wishes to render their power unable to kill, this can be arranged, but that counts as an extra, which will remove the Class decrease.