On a full attack action the Minotaur gets iterative attacks with its greataxe (+9/+4), as well as a secondary attack goring with its horns (+4). On an attack action, it could either use the greataxe (+9) or the horns (+9). If the attack line for the Minotaur read 'Huge greataxe +9/+4 melee; or gore +9 melee' then it would be one or the other and the gore would not be a secondary attack in that case.
While looking this up and comparing monsters in the MM I came up with a question of my own about Multiattack. The description of Multiattack (MM p11) lists that the prerequisite for the feat is 'three or more natural weapons'.
However, I noticed that the Athach and Marilith have Multiattack but do not have three or more natural weapons listed in their attacks. They both have primary attacks with manufactured weapons, and a secondary attack with a natural weapon. In addition, the Lizardfolk can either make three attacks with natural weapons (2 claws and bite) which qualifies them for Multiattack, or they can trade the 2 claw attacks for a greatclub but still employ the Multiattack feat so that they only have a -2 on the secondary attack with their bite.
There is also the case of the Salamander who for some reason is given permission to ignore the prerequisites for Multiattack as part of its description. It seems like even the writers of the MM didn't like the prerequisite for Multiattack.
The FAQ adds yet another case to consider when answering the question on nezumi characters mixing weapon and natural attacks in the Oriental Adventures section of the FAQ. I don't own OA, but judging from the dialogue in the FAQ nezumi have natural attacks something like 'claw; or bite'. If this is so then it seems like they also shouldn't meet the prerequisites for Multiattack yet the FAQ mentions that they could make use of it to reduce the penalties on a secondary attack with a natural weapon while using a manufactured weapon for their primary attacks.
So, possible conclusions?
Judging by the MM examples the prerequisite for Multiattack seems to be 'three or more attacks including at least one secondary attack with a natural weapon'. If the example of the nezumi from the FAQ is taken into account, the prerequisite seems to be 'two or more attacks including at least one secondary attack with a natural weapon'.
The only way I can see to uphold the written prerequisite of three or more natural weapons is if we're supposed to speculate on whether or not a creature has the potential to have three natural weapon attacks even if they are not listed as attacks on the creature's profile. It seems that this has been done in the MM but it I think it is sort of hit and miss as far as satisfying a prerequisite is concerned. For example, you could speculate that even though the minotaur has no listed natural attacks other than its gore it would be possible for it to make two claw or slam attacks instead of using its greataxe, and then also have its gore as a natural secondary attack. This would then satisfy the prerequisite and you could have a minotaur who has Multiattack instead of one of its other standard feats.
I checked the MM errata and the FAQ for possible changes to the prerequisites for Multiattack but both came up blank. I realize that by now I've overanalyzed this beyond all reason, so I'd appreciate if someone could stop my head from spinning and provide some insight on this.
