cool..i was trying to gain pets too after I beat this game :-) sorry that i can't really remember any good pet drops but here are a few i got:
dire ghoul: ghoul pet w/ card from that pig dude where the Death Oni comes out
Rat Magician: rat in some type of tuxedo no card drop from meowiarty in MB i think
Black Widow Spider: ...basically a black widow spider drops from MB from this black widow boss
Didn't get these but:
Jade Oni from the Jade Oni from MS
Sprite from Allicane Swiftarrow in Firecat alley
I think a blue or yellow ghost from General Akkiles from Cyclops Lane
Storm Hound from Malistaire and/or Oakheart (MS)
Fire Cat from some boss in Krokotopia in the chamber of fire pretty sure
Dark Sprite OR Dark Sprite w/ card from Lord Nightshade from Haunted Cave
Evil Snowman from Pop's O leary from MB
Golem (robot thing) from this boss in countereast or wesr from MB
Fire salamander (unknown boss)
Storm Salamander (unknown boss)
Well thats all I can think up rite now but if you want the WHOLE pets list then go to wizard101central.com. search for the topic: pets and theres this WHOLE list lol hoped that help
