Quote Originally Posted by Thrudd View Post
No, you still gain HP. You can't use the abilities of your old class again until your new class has passed the level of the old one. Well, you can use the old class abilities, but if you do you don't get any XP for that adventure. The only thing you have from your old class is the HP and the saving throws, until you've gained enough levels.
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.