Species: Iceberg
Type: Ice
Abilities: Clear Body
Weaknesses: Fighting, Steel, Rock, Fire
Height (ft): 5' 11"
Weight (lbs): 385.8

#378

Pokedex Entry: Regice cloaks itself with frigid air of negative 328 degrees F. Things will freeze
  solid just by going near this Pokémon. Its icy body is so cold, it will not melt even if it is
    immersed in magma.

Luckily this is just a Pokemon, and not something you'll be running into anytime soon on your way to school or work or maybe a trip to a secluded island. 

But if you were somehow magically able to live in the world of Pokemon, managed to travel to the Hoenn region and track this block of ice down, well you'd be dead before you had a chance to catch it. 

That is because your body's ideal temperature is 98° F (36° C). If you so much as drop two or three degrees in temperature your body starts going into hypothermia. At 84° F (28° C) you fall unconscious and at 70° F (21° C) you'll be dead.  And if you were exposed to the -328° F (-164° C) mist that Regice emits from its body, your body temperature would drop so fast you would be a block of ice in seconds. 

All your bodily fluids would freeze. Including your blood, saliva and even the fluids in your eyes. They would freeze and shatter. Rest in peace.

But, even before you came close to the Pokemon itself, you'd probably die in the process of trying to find it. Having to dive deep into the ocean to swim under an island while having zero gear to dive at such depths, your body would be crushed by the pressure or you'd die from lack of oxygen. 

I'm not sure why someone would go looking for this thing, you'd have to have a death wish.

Species: Lava
Type: Rock, Fire
Abilities: Flame Body, Magma Armor
Weaknesses: Fighting, Ground, Rock, Water
Evolves from: Slugma
Ability (hidden): Weak Armor
Height (ft): 2' 7"

#219

Pokedex Entry: Magcargo's body temperature is approximately 18,000 degrees F. Water is vaporized on contact. If this Pokémon is caught in the rain, the raindrops instantly turn into steam, cloaking the area in a thick fog.

This Pokemon is much more common to come across, so, you're twice as lucky that Pokemon are the thing of imagination and Nintendo. 

With a body temperature of 18 000° F (9982° C) its body is almost twice as hot as the surface of the sun. Meaning you wouldn't be able to get closer than a couple hundred meters of this Pokemon. 

Anything within 50 meters of Magcargo would burst into flames, including yourself if a wild one happened to slither out in front of you. 

The rapid change in temperature would cause your body temperature to change quickly and your bodily fluids, all of them, would evaporate. So all the new steam trapped under your skin would burst out, all the while your brain would be boiling, your skin burning and your bones turning to char.

And it would happen so fast, you wouldn't know what hit you. Since you'd ... be dead.