Example: I gave a -6 level cap to Halflings to pay for their +4 save bonus and innate Invisibility. Let's drop the save bonus and focus on the "little people who can hide in plain sight" archetype: that's a -2 adjustment. Under this scheme, a Halfling can turn invisible at will, but must make a Con -2 save or potentially lose up to 4 hit points from the effort (roll 2d6, each die result less than or equal to 2 counts as damage.)
An option to the damage roll, especially for races with multiple abilities at different power levels, is to treat failed Con rolls as causing sleep deprivation, with a penalty to action if it reaches the severe level.
If you trust the original race's power balance, this actually allows quick conversions of AD&D races:
- subtract the race's level cap from 12 to get the level adjustment;
- subtract level adjustment from Con rolls when using innate powers.