Question said:
Weird why would they put it on page 204? Most would totally miss that.
Well, page 204 is where the mount rules are, and page 200 where the leadership rules are. What I find weird is that there are 2 separate rules about the same issue.
Question said:
Okay just checked, that still doesnt explain how the bonus HD from the paladin's special mount abiltiy interacts with leadership though.
If I understand it correctly, it works like this:
Unicorns have 4 HD and a level adjustment of +4. So, they are ECL 8 creatures. If I use the rules on page 200, I have to take leadership AND wait till I can have a cohort of 10th level (because of the +2 LA thing as a cohort) and have to be at least a 12th level paladin. Since there's no mention at all about the bonus HD, AND the character needs a feat, AND use the ECL of the creature I would say it gets the bonus HD of the regular mount of a 12th level paladin (that is +6 HD).
Now, comparing to the rule on page 204, I just have to be a 6th. level paladin and get a unicorn as my mount. By 12th level, using the table on page 205 it gets +6 HD (Level +6 line) and didn't have to spend a feat or use the ECL, instead I just had to wait one level.
Let's take a look at the griffon:
1) Page 200: Griffon's ECL = 10, and as a mount with leadership is ECL 12. So, a 14th level paladin can get it with +6 HD, and a 15th level paladin can get it with +8 HD.
2) Page 204: Griffon can be taken at 8th level. So at 14th level, it gets +6 HD and at 15th level it still gets +6 HD.