Damaging terrain can take various forms, but all are hazardous to step into unless the Wading Boots are worn or the Wonderwing is being used. Most hazards cause damage every four or five seconds; in this time Banjo can get out of the substance without being hurt more than once. Banjo usually cannot move very fast in hazardous terrain.
Freezeezy Peak's pools of water are far too cold to safely swim in without a thick layer of blubber. The water is just deep enough to force Banjo to paddle, so at least he doesn't take any fall damage from it. The water on Hailfire Peaks' Icy Side is just as cold but not as deep.
Some (well, half) of the sand in Gobi's Valley is superheated by the desert sun, burning anyone who falls into it. A certain portion of the sand can be destroyed once its surfaced is filled in with water.
In Mad Monster Mansion and Click Clock Wood are spiked plants that cover parts of the ground. The thorns in Mad Monster Mansion are somewhat rare, while the entire patch of ground in front of Mumbo's Skull in Click Clock Wood is covered in brambles. The brambles die during winter and have no effect on bees.
Large areas of Mayahem Temple and Terrydactyland are flooded with quicksand. The quicksand itself is not dangerous, but the Dragundas living within are. Dragundas also appear in the poisoned water around Grunty Industries. The quicksand in Mayahem Temple does not damage Banjo constantly; it instead flings him out. The Wonderwing has no effect in avoiding these terrains.
The Fire Side of Hailfire Peaks is covered in molten rock. Swimming in it is not highly recommended.
Banjo and Kazooie can't breathe in anything but normal air, so entering another fluid can be dangerous.
While water by itself is no hazard, staying underwater too long definately is, and such is unavoidable in Clanker's Cavern.
Oily Water/Icy Water
Rusty Bucket Bay's resevoir is full of oil pollution. Simply swimming in this "water" reqiures holding one's breath, and diving underneath uses up air twice as fast. The water in Clock Clock Wood's winter has the same properties.
A large green pool in the corner of Rusty Bucket Bay contains this dangerous material, which is so toxic that it attacks both Banjo's air meter AND health bar.
While Banjo and Kazooie are not physically limited in any way by toxic gas, they have to leave the area before their air meter depletes. If such happens, then health is constantly lost until fresh air can be taken in. Toxic gases of various kinds appear in Glitter Gulch Mine, Grunty Industries, Hailfire Peaks, Cloud Cuckooland, and the Hag 1 battle. While most toxic gases cause normal air loss, a certain gas in Grunty Industries is so dangerous that air is lost two or three times a second.
If the bear or bird get violently forced between two solid objects, their health plummets to one or two honeycombs. A second hit finishes the job. The Wonderwing can protect against most crushers.
King Sandybutt's Tomb
If Banjo and Kazooie cannot find their way out of the maze in King Sandybutt's Tomb, the spiked ceiling drops in on them. This crusher doesn't need two hits to do the damage and cannot be avoided.
Found in Glitter Gulch Mine, these relatively weak crushers only do 1 honeycomb of damage. They must be shut down so the Jiggy Boulder can be mulched up.
Trash Compactor and Wall Crushers
While the Trash Compactor on Floor 1 of Grunty Industries is much the same as Stomponadon, the Wall Crushers can't be bypassed (even with the Wonderwing) unless Mumbo gives them an EMP, allowing Banjo and Kazooie to pass.
Banjo's leg bones can't take the stress of impact from too high up, so leaping off a cliff will likely lead to pain. Using the Feathery Flap can help prevent this, but not for very high plummets. Kazooie alone can Feathery Flap indefinitly to avoid this problem, but is still vulerable to fall damage. The FALLPROOF cheat in Banjo-Tooie deactivates fall damage, but doesn't prevent fall helplessness (the inability of action during a long fall). Falling into water deep enough to swim in does no damage.
While burning stuff can certainly be useful, it's generally a bad idea to touch the flames.
Beak Bomb misuse
Flying like a missle can have its benefits, but if Kazooie misaims and rams into something indestructable, there could be a medical problem. Especially if the momentum of a ground impact leads to sliding off a cliff.
Toxic Gloop/Boiling Water
Vats of dangerous chemicals can be found in Grunty Industries and Cauldron Keep, while pools of boiling water exist on the Fire Side of Hailfire Peaks. Jumping into either causes the jumper to be flung towards land. Banjo can safely float on the surface or dive underneath if need be.
A certain Jinjo in Hailfire Peaks is trapped by this impassable wall of scorching liquid. The Wonderwing is the only way to get through.
Cauldron Keep is protected by a series of electrical gates that not only prevent entry, but injure would-be tresspassers.
Rusty Bucket Bay, the Top of the Tower, the Isle O' Hags, Terrydactyland, Hailfire Peaksl and Cloud Cuckooland all have edges without ground below them. Falling off a cliff in such a case leaves it all to gravity. (Note: In Banjo-Kazooie, all bottomless falls incorporate the "fell into lava" sound effect.)