Well-designed monsters are fun to run, and fun to fight. (Part 2)

Running powerful monsters is one of the great joys of being a DM. Hopefully, I don't have to tell you to imagine stomping around the battlefield as a 10-ton treant, or strafing puny PCs with your iron tail spikes as a manticore. (If you have to imagine this, try DMing as soon as you can!)

The problem is, sometimes the rules for trampling enemies aren't laid out very well, or worse yet, the rules for flight aren't even in the monster book you have in front of you. Many (maybe most) battles include special cases that aren't explicitly covered by the rules--for example, what if the party being trampled is wearing spiked armour?
Even for seasoned players and DMs, having to search for a rule elsewhere slows the game to a dead stop. Worse, page-flipping can sometimes result in discussions (which can be healthy, but they always ruin the flow), or even arguments, neither of which are as fun as resolving the action and continuing play. (The trample example above would likely have the players looking up armour spikes in the PH and the Trample special attack in the MM and DMG--three books for one rule!)

A well-designed monster will have all but the most basic rules at your fingertips, reducing page-flipping, discussions, and arguments, and maintaining the flow of the game. You get back to the fun quickly, if you ever left it at all.

If your critter has any special abilities, know the rules in advance so you can ask for the appropriate rolls and present the players with their options. A simple shorthand version of the attack form, like "Trample: (Page XXX DMG) Move 40 feet, 1D10+12 damage, DC 20 Ref Save for half *OR* Take AoO (AC 24)" can speed up the actions on your side of the screen, and will let you resolve any unforeseen issues as quickly as possible.