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Environments the trainer can't go normally without protective equipment and recommended Pokemon-types who won't sustain damage from the area.
Dragon, Fire, Ground and Rock types can go into volcanoes without being burned. Water types need to activate Aqua Veil.
Poison and Steel Pokemon can resist polluted areas. A certain held item can help your other Pokemon though.
Electrified areas can take any Pokemon, but do keep a Ground or an Electric type around offset lightning strikes. Most Steel types are not recommended as they INCREASE the frequency of lightning strikes
Sandstorms can by blown away by Flying and Dragon types, otherwise keep a Rock, Steel or Ground type handy.
Haunted areas will have unidentifiable ghosts without special equipment. Dark types will prevent surprise encounters, though.
