Quote Originally Posted by Mark Hall View Post
You also usually don't get new HD, either, until the new level exceeds the old... but Bard's are a special case.

So, you want to powerplay your 1e bard? You start as a fighter, naturally, and go to 7th level, meaning you have 3/2 attacks and 7d10 HD (plus 7 times your con bonus). You then continue to 9th level thief, getting 2 more D6 in HD (and your Con bonus twice more). Now you switch to Bard, and the fun happens.

Bards get 1d6 HD at levels 2-11, for a total of 10 extra HD... meaning a Bard can, conceivably, have 19 HD, which will be 7d10+12d6 (or 7d10+2d6+10d6, to give the class breakdown). Since you get your Con bonus on EVERY hit die, a bard who had a 18 Constitution would have an additional 76 HP, on top of that MASSIVE number of HD.

Toss in UA and you can also do this while getting the advantage of double specialization.
Yup. The bard is special in that bard levels and hit dice. The fighter thief dual class part remains the same.

As to his other bit PHB page 33:

At such time as the character has attained a level of experience in his or
her new class which exceeds the character's former class level, the following
benefits are gained:
1. A hit die appropriate to the new class is gained for each
increase in level of experience, up to the maximum normal for
the class in question (and thereafter hit points are likewise
gained), and
2. The character may mix functions freely and still gain
experience, although restrictions regarding armor, shield,
and/or weapon apply with regard to operations particular to
one or both classes.