Slimes don't run in low health and summon more slimes to overwhelm their enemies with strong melee attacks. They move items out of their way, but dont kill weak creatures. A slime will never retreat (they fight until death).
The summoned slimes are weak against ice damage +10%. Slimes are useful to level because they have relatively low hp and give good experience. With 55 shielding you could train with slimes successfully. Watch out! They can kill low levels very fast if they get trapped, especially mages, if you get trapped by 3 or more, try to kill the "motherslime", you can know which one this is because of the blue sparkles around it.
A good tactic is to mark the slime that summons the others as only the original will do this. When a slime summons, you will see the blue shimmer of a spell being cast. If you can't pick out the original while you're attacking, don't hesitate to start attacking the next slime. Though at times you will find that your second target is only a copy and it will disappear if the slime you killed before it was the original, it is better to be safe in case the first slime is not the original slime.
Knights can easily kill these creatures because they have really weak defense. Try to attack them in narrow passages where only two slimes can attack you (they have strong attacks and three or more will break your shielding).
Paladins: Just attack them and don't get cornered. Try not to lose the real slime so you don't waste Arrows/Bolts.