I've been on this site for a few months now, and there are many things to like about it. Everyone is very polite and helpful, there's no shortage of things to collect and earn, and I love all of the pets and costumes! Below are just some costume and pet ideas I've been thinking about, in no particular order. Except alphabetical, I guess.
Costumes
Apex Pets wear cool racing helmets and fireproof racing suits
Arctic Explorer Pets wear many layers of thick coats, a scarf, and goggles.
Bladerunner Pets appear cybernetically enhanced, as if they are from one hundred years in the future
Centurion Pets wield swords and are clad in Roman armor with giant plumed helmets.
El Presidente Pets stand up straight and tall, wearing a giant officer cap and a highly decorated military uniform.
G-Man Pets are clad in form-fitting black suits and dark shades, wearing stoical or sneering facial expressions.
Grease Monkey Pets are clad in oil-stained jumpsuits with wrenches. Could be given as a rare bonus prize for completing Garage Quests.
Hazmat Pets are clad in very bulky hazardous material suits, surrounded by barrels of nuclear waste.
Mercenary Pets wear baggy camoflauge trousers, ammo belts, and have gruff beards if male.
Metalhead Pets have outrageous hairstyles and are clad in denim jackets and white hightop sneakers.
Pinfall Pets wear flashy and cheesy professional wrestling outfits, masks, and championship belts.
Post-Apocalyptic Pets are sooty, wearing gas-masks and makeshift armor made of stop signs, license plates, chainlink fences, etc.
Russian Pets are colored like the Soviet national flag and wear ushankas on their heads.
Statue Pets appear to be Roman carved statues of themselves. Could be given as a rare bonus prize for completing Simerian Quests.
Pets
Anubis A sitting jackal with a cool mask.
Chol A majestic and wise phoenix, always white regardless of color, yet costume colors effect the sparking flame surrounding it.
Conqueror A gigantic, Godly Worm, wrapping around a miniature version of the entire world of Marada. (Named after the Edgar Allen Poe poem of the same name.)
Custer A horse dressed like to a Civil War officer, similar to a Gonk but more gallant and standing on all four hooves.
Engenakunqandeka A muscular gorilla with a disproportionately large torso. (Name means in "Unstoppable Fury" in Zulu)
Entombed Some form of terrifying zombie-like creature, holding up a sign with a smiley face painted on it to cover his own face.
Fashinne A very stylish chameleon with a top hat and a large curly tail
Hendrix A cute fox that stands upright on its hindlegs and has large fluffy ears.
Genghis A mustachioed snow leopard from Mongolia with a bow and arrow, perched atop an armored Gonk.
Grotesque A living Gargoyle perched atop a cathedral archway.
Iktomi A hairy tarantula the size of most television sets.
Leviathan A Plesiosaur whose body is encased within the sunken hull of a battleship.
Naga A vaguely humanoid reptile with a serpent-like lower half.
Pestilence A giant, man-sized locust that is strangely cute.
Platemail A very tiny armadillo completely covered in incredibly large armored spines
Rosebed A tall, sleek Ocelot, sitting upright and incessantly glaring at you.
Sessho-Seki A rock formation with an ominous aura surrounding it.
Slayer A foreboding but otherwise adorable sheep with absurdly large, curved horns