Sorry for the slow response again. Hurricane recovery here has been a bit, “challenged” I guess is the word. Our internet went out again 2 days ago and there’s no indication as to when it’ll be back so I’m responding here on my phone.
Codex was designed specifically not to need a grid or miniatures. We developed it before the proliferation of some of these new online tools like Roll20, one of our playtester groups for monsterberg used that. I don’t know the details of how they coded it in their system but onset means everything up to the outermost striking range for a handheld weapon. Therefore it would actually be a different physical distance depending on the weapons you had, the base for 3.x OGL as I understand it would be two 5 ft squares for a reach weapon or one 5 ft square for an ordinary ‘melee’ weapon. In codex a pike or lance could be twice that. It just depends how granular you want to get.
The general rule of thumb on skill checks is that if you’re rolling a “one die” skill check, it costs no MP. You can spend an MP to add an extra die to a skill check like to give yourself advantage in 5e terminology. A feint is kind of an interesting outlier or special case, because the assumption is that you’re making some kind of physical effort to trick your opponent into thinking you’re attacking.
The Failer is kind of an ” Attack Feint” you make an attack, it’s intended to be a feint but if they don’t defend, you will probably hit them. If they defend overzealously you can trick them. Their focus and momentum shifts in one direction and you attack in the other. I’ll post a pretty good example for some tournament footage it’s super fast so it’s hard to see what’s happening even in slow motion but if you wanted a couple times you’ll get the idea.
So for the failer no there’s no extra MP cost for the feint. The initial attack is the feint. It’s definitely an advanced technique which requires good timing and proprioception (which is basically covered by the CHA modifier in OGL). If done properly it’s extremely effective. In practice it’s a little bit like the Zucken, but with more emphasis on the bluff and less on the fuhlen, since ideally you won’t even make contact with their blade (you might, but probably very lightly).