"M" is for "Muckripper"

Muckripper

No. Enc.:  0 (2d8)
Alignment:  Neutral
Movement:  90' (30')
     —Swim:  90' (30')
Armor Class:  5
Hit Dice:  8
Attacks:  1 (bite)
Damage:  2d8
Save:  L4
Morale:  9
Hoard Class:  None
XP:  3,560

Muckrippers are bloated, 15' long, amphibious fish that congregate near the most toxic of pools, favoring ruined water treatment plants, slurry pits, and industrial retention ponds contaminated with heavy metals.  Highly aggressive, they usually charge head-on, but also conceal themselves beneath the mire to ambush passing prey (Surprising on a 1-4 on 1d6). Pods of muckrippers even chase victims up trees, and then gnaw through the trunks until they collapse....

Muckrippers disgorge glowing gobbets of filth [Radiation Class 5-10; determine at random on 1d6] at distances up to 25'.  They are obviously immune to all poisons, disease, and radioactivity. 

Mutations:  Dermal Poison Slime, Toxic Weapon ("Toxic Glob")