No mobs will spawn on peaceful, you may hear noises but they will be effects even on peaceful. the only entities that spawn in peaceful (not including the nether or the end) are players and animals unless, in the end or nether.
You may have your difficulty set to Peaceful. Monsters will not spawn in Peaceful mode.
If the difficulty isn't set to peaceful, mobs will spawn in creative mode.
Yes, wolves spawn even on peaceful mode.
Yes
There are no hostile mobs in Peaceful difficulty mode on Minecraft. Mobs such as creepers, skeletons, zombies, spiders and all other manner of hostile mobs do not spawn while Peaceful mode is active, though you will see (in dark places or at night) mobs attempting to spawn and immediately disappearing a millisecond after appearing. Mobs cannot attack you regardless unless another difficulty is triggered.
All hostile mobs spawn on easy difficulty.
It does when its not in Peaceful mode i think
Slimes still spawn, but only within 15 blocks above bedrock (adminium) and in large cavernous areas. If you dig down really far, and find a nice big area within 15 blocks of the bottom, you might find slimes. Another thing about slimes, is they spawn on any difficulty, including peaceful, but only the small one's will spawn on peaceful. There's a glitch where big slimes don't de-spawn when you change the difficulty.
Peaceful mode means that no monsters spawn, so there will be no Slimes.
Get single player commands then type in spawn silver fish. Make sure it's not on peaceful.
Yes, but the Pigmen and Ghasts won't spawn.
You probably have it on Peaceful Mode thats the only reason I can think of.