I skipped a few posts during the 30 Day Challenge, but thought I would make them up here, for completeness, to satisfy the curiosity of my readers, and because I find the Challenge's questions neat.
Day 21 - Favorite Dragon Color/Type
My favorite dragon is the Fang Dragon, originally debuting in the Forgotten Realms setting, if I'm not mistaken.
The fang is appealing to me because it wants to engage you in melee. While most dragons, at least in my mind, would rather send minions into hand-to-hand and play the range game with its attackers/its victims, the fang dragon is at its most deadly in close range.
The bite of a fang dragon drains Constitution, weakening the opponents it has in front of it, and making for an even quicker death of its foes. Judicious use of its sound imitation ability can facilitate up-close fights and its trip ability ensures that once the fang dragon has you in melee, it will be hard to get away.
Not only all this, but don't forget that the fang dragon is still a true dragon, and as such still have frightful presence, high spell resistance, multiple attacks, insane ACs and spell-like abilities, as well as casting ability like a sorceror and damage reduction.
They might not be as smart as some other dragons, but ferocity more than makes up for it.
Day 22 - Favorite Monster Overall
This one is harder to do, since the Challenge asks you to list quite a few favorite monsters by category. Obviously, I feel like I can't use previous answers, though wouldn't one of them be the favorite overall?
I'm going to be interpretive a little with this one, and append "that I've used in a game." This makes the choice quite a lot easier, as there are two monsters that I fall back on time and again. The first, and would be winner is the zombie, but I'm not including it, as I haven't used it in a long time, and it seems like cheating to do so when their use has declined, and so I'm going with the lowly goblin.
Goblins are just fun. Creepy little craven psychopaths that, unchecked, will eventually overrun and corrupt any place they call home. Goblins, like any other humanoid, can fit quickly into any niche you need at the time, as they can be any class you would like. Need a spellcaster? A goblin shaman or pyromancer might fit the bill. A couple of goblin shadow dancers could quickly wear the party down by forcing use of resources, eventually routing even a somewhat prepared party.
They can be as cunning or as stupid as you would like, and are usually fun for your players to bash, as well.
Day 23 - Least Favorite Monster Overall
This one comes from not only my experiences with it as a DM, but also because of my opinion of the thing as a player. My choice for least favorite monster has to be the mimic.
Perhaps my friends and I don't follow some unwritten plan somewhere, but no party we've ever been in that has encountered mimics has ever truly been that successful against the things. Sure, we eventually defeat them, but the seemingly insane amount of hit points coupled with their annoying adhesive abilities usually sees the party struggling by the end of the fight.
We never have solvents of any kind to break free and our characters can never seem to roll well at all in any aspect of a fight with these monsters, so I'm just not a fan. Nothing about them are fun to me.