Having once of the stranger names for a magical beast (and that's saying something), the rakklethorn toad actually doesn't really have much to it. It's CR 1, and it excretes a Dexterity-hindering poison from the thorns that stud its back. Oh, and said thorns can be launched like projectiles, so I guess there's that.
What is it with rats and getting so many variants?
...Actually, thinking about how prolific rats are, it kinda makes sense, but still.
In any case, barrow rats are CR 1/4 Magical Beasts that, as their name implies, hang out around barrows and other places where carrion is easily attained. They are obligate scavengers, feasting on whatever corpses they can find and taking whatever's left over with them in bits and pieces. Their only supernatural ability is stoneskin as an SLA as a defensive maneuver against predators. In other words, they are interesting set pieces, but as-is there's not a whole lot to justify their existence or explain their role.
These horrendous CR 10 undead are the personal court jesters of Orcus, demon prince of the undead, and are just as humorous as that title would imply...in other words, absolutely terrifying. First off, dressing up a ghoul in a jester's outfit doesn't really mask the fact that it's a razor-toothed undead abomination, so its appearance isn't exactly the most pleasant. Then you add in its ability to induce fear with a cackling laugh or bash you with its masterwork light mace...but make you laugh uncontrollably as it painfully blugeons you with this enchanted device. Of course, if that isn't enough, it can also use a deck of many things on people as a ranged touch attack. And the worst part? These things are supposedly typically sent to "humor" Orcus's favored. Now imagine what they'll do to you if you aren't in the demon prince's favor.