right! guess I messed that up mistaking all feats for chosen at level12 (where I made the character). newbie-mistake right thereAt 12th level a warlock gets the following breakdown of invocations:
Least - 3 (Baleful utterance, Entropic warding, spiderwalk)
Lesser - 3 (hellrime blast, eldritch chain, flee the seen)
Greater - 1 (chilling tentacles)
Dark - 0
I am not sure how the helfire warlock adds to the mix but I am assuming it is a +1 level for invocations which makes it the same progression as a warlock.
Also extra invocation allows adding an extra invocation of 1 level lower than normal. Can't take it until at least 6th level (which grant 1 more least invocation, 11th level to get an extra least - a 12th level warlock can't gain an extra greater). So taking the feat twice would be your 6th, 9th or 12th level feats. So you could get 2 least or 1 least and 1 lesser. Can't get both eldritch chain and walk unseen {invisibility} using the extra invocation feat.
Extra invocations:
Walk unseen {invisibility} - lesser using 12th level feat.
XXXX - least using 6th or 9th level feat

But even though I mixed things up, it still works, right? Just a little differently from what I wrote above (btw: yes, Hellfire Warlock progresses Invocations just like the Warlock base class):
invocations normally gained (not through the extra feat):
least:
- baleful utterance
- entropic warding
- spiderwalk
lesser:
- hellrime blast
- eldritch chain
- flee the scene
greater:
- chilling tentacles
gained through extra invocation feat:
- walk unseen (lesser)
and this actually leaves me with TWO more feats I have yet to spend since so far I only used one for Maximise SLA (Hellfire Blast), one for Extra Invocation (Walk Unseen) and the two Abyssal Heritor feats. Saved me one feat as opposed to what I wrote in my last post. Damn so I still have to decide on 2 feats lol (not that I couldnt find something useful, its just that I'm trying to figure out which would make the most sense for me)