Monsters are, by definition, not very nice.
Some monsters are nice, but this is because they are also usually Muppets. Most monsters are vile and dangerous, but a few are actually misunderstood, such as the Flatwoods Monster, the Loch Ness Monster, or the Purple-Headed Monster (though being misunderstood does not always mean they are nice or will not eat you). Many are morally ambigious tricksters who delight in confusing humans by alternatingly helping and harming them, such as Yokai, genies and the Sphinx. Others still are mindless death machines, whether they are zombies, P-zombies, volcano zombies, zombie snails, zombie dinosaurs, or gnombies.
Isnashi, Leucrota, Amphivena, Chariblur, Graboids, Skinwalkers, Noseworms, Snallygaster, Bloodworms, Yeast, Nopefish, Tooth Rot, Guitar Monster, Skeletons (redeadened) and the Rhode Island Monster (deceased)
is a very expensive service as it can be a huge undertaking so don't ask the Revengreists!!