Do you want more mobs and trouble? Here it is! The More Mobs Addon created for this reason and not for other dumb things - don't worry! This will have a few updates and adds many mobs into the game.
Select version for changelog:
Changelog
Nothing interisting...
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I have some suggestions:
-wild animals (butterflies, hedgehogs, goats, deer, etc)
-small spiders
-firecreeper (will only appear in the Nether)
-variety of colors in the chicken models
-And mining and lumberjack zombies