Why hello there, young trainer. You look quite fatigued. Why don't you take a little rest here? No? You want to look for Slowpokes? Let me tell you, those Slowpokes are quite aggressive nowadays, ever since those Rocket fools came bumbling along. Here, take a drink of water, while I tell you how dangerous those Pokémon are.
Many Slowpokes lived in that beautiful grassland. All happy, content with the lazy life they had. Until a group of men clad in black came along, obsessed with their tails. Chop. They took a tail. Chop. They took another tail. These men stole tail after tail, leaving the Slowpokes groaning in agony when they took the tails.
Some Slowpokes died from the sheer pain of their tails being forcefully taken. However, the rest that lived bore a strong hatred towards the ones that took their tails. Slowly, they began to grow fierce, and even more untamed. The men still came, able to snatch a few tails every now and then.
Until one day, one of the Slowpokes managed to strike at the wicked men. The Slowpoke forced a man on the ground, then tried to look for his own tail. Unfortunately, there was no sign of his tail. The Slowpoke, being an average dim-witted Slowpoke, simply ripped the man's arm off, substituting the arm as his tail. The arm worked well for a tail, and the Slowpoke began to spread news about this new way to get tails.
The Slowpokes with missing tails pounced on every person that was clad in black, believing it to be their enemy. They would rip off their arms and legs, and strut off with them happily.
Then why, you would probably be thinking, do you not see any Slowpokes with arms or legs as tails? That's simple. The Slowpokes love to swim, you see. They would go into the water straight after they acquired their new tail, and test out its capabilities in water.
That's when the Shellders strike. You probably know that, according to theory -- a Shellder clamps itself onto a Slowpoke's tail, and Slowpoke would evolve into Slowbro. Well, that's exactly what happened. The Shellders loved the taste of human meat so much that it would do anything to stay there forever. Of course, the Slowbros didn't mind, for the Shellder gives it strength.
Once, a trainer accidentally cut off the arm from a Slowbro. The Pokemon was so enraged, it snarled and hissed, and its power manifested greatly. The trainer was immediately killed, his arm ripped off for compensation. The Shellder then clamps back to the new arm.
Slowpokes aren't meant to be trifled with, trainer. If you want to fight with one head on, I hope you don't use your arms much.