So if I were to make a new hammer trick, I should require Hammer Mastery, yes?
I think it would depend on the trick's effect and overall potency. If the new trick can only be used with hammers, I'd certainly consider the benfits of including Hammer B/M/S as a prerequisite, but I don't think that should be presented as a hard and fast rule.
Either way, I'd prefer for C-c-c-combo! to introduce the minimum number of restrictions on tricks beyond the trick's own text, including prerequisites. The "must pick a specific spell along with a spellcasting trick" is already going to be annoyingly wordy, but the reality is that the spellcasting check is the only check in the game that has a whole chapter devoted to all the things it does
. Its really sort of an umbrella description for about 250 different checks.
Directly on the subject of combos, can you take other free actions with a combo. Knife Mastery lets me fient as a free action. Can I do so in the middle of a combo or do I need to build the fient into the combo?
While slightly worisome, unless a more terrifying free action is put forward I'm prepared to continue allowing free actions to come and go as the please rather than add even more verbage to block it.
Also, the way I read the feat the first trick determines what sort of action the combo takes.
Would it be better to instead say that the combo takes the same action as the longest component? Frex, Back at you! - Mixup(Bullrush) is a flavorful combo but it looks like it would be a free action. Is that right and if so intended?
Both are correct and intended. The -5 penalty is the is the drawback for having a full action folded in, and back at you is still reliant on someone else handing you a trigger. After getting that bullrush in the face for flinging things at you, people may stop flinging things at you