In SLASH'EM, the monster glyph z is for [z]outhern or Australian animals, the zruty having been moved to the apelike Y monster class. Below is an overview of the monsters in this new class, all modeled mostly after real-world counterparts. All have a chance to be peaceful if you are neutral, except for the Tasmanian devil.
Echidnas are generally the first of the 'zouthern' animals seen; they are not terribly threatening, being rather slower than most animals, and doing comparatively little damage.
A platypus is a slightly dangerous monster, having a poisonous kick. It is still somewhat slow, and can be easily taken out with ranged weapons if the poison is a problem.
The real platypus is really poisonous. It has a poisonous sting at his hind legs.
A koala poses no direct threat to you, possessing no physically damaging attacks of any sort. Its calming touch will abort any active techniques, but is otherwise harmless. However, other monsters affected by it will turn to peaceful (although some monsters may resist). It is thus a large threat to any pet, since a peaceful monster is no longer your pet, and some may be difficult to tame again, particularly polymorphed pets. A pet koala, however, is very useful, since it can turn hostile monsters peaceful. They are somewhat slow and not overly strong, however. They can be tamed with, and will only eat, eucalyptus leaves.
A wombat is a rather unextraordinary monster, being roughly equivalent to a wolf in terms of difficulty, and having no particular distinguishing attributes.
A Tasmanian devil can eat organic items and engulf non-organic ones, much in the manner of a gelatinous cube. This is likely a reference to Taz from Looney Tunes. Like most SLASH'EM monsters, it is somewhat more dangerous than vanilla monsters that appear at the same time.
A wallaby is a moderate danger, having a speed slightly greater than that of the player. It is roughly equivalent in danger to a unicorn.
A wallaroo is somewhat of a threat during the midgame, owing to its tendency to hit reasonably hard and fast, and appear in small groups.
Kangaroos are quite a large threat through SLASH'EM's mid- and even late-game, since they hit very hard, are twice as fast as a player without speed, and tend to appear in groups. Note that they have no magic resistance, making sleep a very valid option against them.