I know that there are options for custom skills, but I have never made a serious attempt at thinking of any, until now! (cue Daeglan)
My idea was related to Mass Combat, I am a strategy game junkie, so it seemed right up my alley. It is really only useful in specific campaigns or character builds, but there is a way to make it more generally useful.
My propose custom skill is this: Strategy (int.): Right before the first roll of Mass Combat (and re-rolled later at GM discretion), make an opposed Strategy check with the opposing commander, success grants one upgrade to your pool, failure grants one upgrade to you opponent's Mass Combat pool (+1 per 2 additional Success/Failure). 2 Advantage/Threat may be spent to remove a Boost/Setback, 3 Advantage/Threat may be spent to downgrade your opponent's Mass Combat pool once, Triumph/Despair may be spent to decrease and downgrade your opponent's Mass Combat pool once.
Dejarik: Opposed Strategy check, must win 3 checks to win the game: 2 Advantage/Threat add a Boost/Setback, 3 Advantage/Threat downgrade opponent's pool once, Triumph/Despair ?
What other examples of custom skills do you have? What critiques do you have of my Strategy skill?