I'm currently involved a bunch of BBEG battles while simultaneously prepping to run an 8-player lvl 20 adventure at GenCon, and so I'm thinking about the ever-popular "kill the boss" type of fight. Wanted to collect any ideas others may have and share my own. I know this is a perennial topic and thread, but eh.
TIP: BBEGs always get killed faster than you think. It's obvious if you think about it; the BBEG always appears bigger, faster, meaner, etc. (hence the BB part of their name) than any other enemy, or just as often they're the only enemy, so the PCs don't hesitate to unload dailies, pull out that potion they've been saving, try crazy stunts (and inevitably roll a nat 20), etc. It's the main reason I never mind OPing a boss.