Limitation is on the master list of Powers. For convenience, here's a copy-paste.
LIMITATION [+varies]
Description: Your abilities are limited in some way.
Note: Suffering from the negative consequences of taking this Power will often, but not always, be a Compel. If the importance of this Power changes during play, it might be necessary to change its cost or compensate with Compels.
Skills Affected: None.
Effects:Limited Powers. Attach this Power to at least one other Power that you possess. Then, select a circumstance. Whenever that circumstance applies, you are treated as though you did not possess the attached abilities.
Rebate. This Power reduces the Refresh cost of the attached Powers. The percentage that the cost is reduced by depends upon how commonly the limitation on your Powers will cause problems for you.
- If it will matter rarely (perhaps once every 6 sessions or so), reduce the cost by one-sixth.
- If it will cause problems from time to time (in some, but not all, sessions), reduce the cost by one fourth.
- If it will be a frequent impediment (once a session on average), reduce the cost by half.
- If it will prevent you from using your Powers except in unusual situations (no more than once a session on average), reduce the cost by three fourths.
At the GM's discretion, difficult-to-classify limitations might grant a rebate in between two of the suggested ones. Decimal costs should be rounded to the nearest integer, with GMs rounding halves based on what cost seems more appropriate.
Most of its development was on
this thread, back when it was still named The Catch. The final touches were put on it in the Custom Powers Master List thread, IIRC.
I'd be happy to see Toughness lose the "mandatory Catch" bit, but by the RAW it's pretty clear that even Inhuman Toughness needs a Catch.
EDIT: Oops, ninja'd.