The scenery in games has been known to do awfully strange things. For example, say you're finishing up a sidequest. You've just found all three sacred stones and put them next to the magic fountain. As you walk back to collect your reward, everything seems normal— What the hell! Since when did that harmless bush have spikes?
The Suddenly Harmful Harmless Object is a monster that is usually part of the scenery, or at least something benign, much like the Wall Master and Chest Monster. It becomes dangerous as soon as a certain condition is met. Usually, they become harmless again the moment the condition is no longer met, although it's sometimes permanent.
These can be used for several purposes. Sometimes, they're used to prevent backtracking, to make an easy area more dangerous, or to make subsequent playthroughs of the game more difficult.
Compare Empty Room Until the Trap.
- In Age of Mythology, typing "FEAR THE FORAGE" into chat grants you a god power that turns berry bushes into sentient berry monsters to do your bidding.
- Blobbz Online has Nightmare Mode, where trees and birds, which are harmless in normal mode, can kill you.
- Cave Story has sixteen sky dragon eggs in the Egg Corridor. These appear normally (and are completely harmless) before you go to the Labyrinth. After you complete the Core and the Waterway, and regain access to the Egg Corridor, all the eggs have hatched, and most of the survivors are now dangerous zombie dragons.
- There's also that door at the beginning that is a disguised enemy, the only one in the game actually. You might not even realize it since it's so sudden and so early.
- Contra III: The Alien Wars has the alien dogs in the background of the first stage. Move past them, and they'll stop eating from the garbage and chase after you. They return in the City level of Contra 4.
- In Donkey Kong Country Returns, on Sunset Shores, the player is given a chance to enjoy the scenery before the Difficulty Spike. Or at least it seems like it, until bushes uproot themselves & chase after you.
- In Don't Starve every time you chop down an evergreen, there's a minute chance a nearby one will transform into a hostile Treeguard.
- Both Dragon Age: Origins and Dragon Age II have statues and suits of armor coming to life sometimes to attack the party.
- Eversion has this with the flowers. The flowers remain more or less part of the background until 5-6, where they become spiky and are instadeath.
- The water may also count. in 4-5 and later, the famous demonic hands appear from the previously much less terrifying water.
- Those strange rocks from Level 5 become harmful in X-7, and then become actual demons in X-8. note
- Final Fantasy IV gives us a dungeon full of demonic doors. Well, they stop actually being so sudden after you fought quite some, and that's exactly when you are rather surprised about one suddenly HARMLESS potentially harmful door. In the same dungeon you end up fighting A WALL as its respective boss. After a dozen doors that's not a surprise even.
- Kingdom Rush series:
- The original game had the Pit of Fire stage where you see a sleeping Cerberus at one corner of the screen. It stays asleep until the final wave, after which it wakes up and attacks you as a Mini-Boss-level enemy.
- Frontiers has the alien eggs in the Lost Jungle that start hatching out Parasytes after a certain wave passes, and Beresad in Beresad's Lair who starts out sleeping but will then start burning your towers to temporarily disable them.
- Vengeance has the mech factory in Clockwork Factory which lies dormant for the first 7 waves. At the start of wave 8, a Dwarf pilot waddles into it, mechanical arms start moving into the factory as sparks fly, and then a MechaDwarf MK.9 slowly marches out as the first Giant Mook of the game. This sequence then occurs periodically for the rest of the waves to spawn more MechaDwarf MK.9s.
- Remember those statues that you've been passing by the entire time in that tower in The Legend of Zelda: The Wind Waker? Well, they turn into massive, spiked harbingers of death at times.
- In Sector 2 (TRO) of Metroid Fusion, all the larvae crawling around the place retreat to cocoons and become harmless after you obtain the high-jump boots. When you revisit the level later after the reactor core has gone offline, you'll find that all the cocoons have popped and released dangerous mutant insects.
- The Flaming Sword in Level 12 of Prince of Persia 2: The Shadow and the Flame.
- In Puzzle Quest 2, some gameboards have solid 'bricks' that cannot be moved or interact with anything. All they do is get in the way a bit. Perfectly harmless. However, some enemies (specifically, most Undead enemies) can use a move called 'Wake The Dead' that causes a random 'brick' to turn into a lethal 5 Skull - without ending their turn. The move is cheap, too, so you can easily end up in a situation where the enemy uses it three times in rapid succession, turning a harmless wall into a heavyweight 15-base-damage attack.
- Dead zombies in the remake of Resident Evil. If they're left unattended without burning the corpses or killing them by decapitating them (for some reason you can't spend a few minutes doing it with the combat knife) they come back as "crimson heads". Not to mention pretty much any corpse could potentially "wake up" if the right plot event occurs.
- In Sacred, assuming you have equipment that allows you to attack animals, a bunny or other innocent creatures can become a deadly foe if your level is low and the difficult settings are at maximum.
- Shivers has evil spirits known as the Ixupi, which hide in different materials. Every time you enter a room, it's possible that an Ixupi could be lurking there. One minute, you're looking at a pile of ashes; the next, a monster jumps out of it and bites you.
- The second Spyro the Dragon game has a cruel yet funny example in Fracture Hills. The level is scattered around with bushes and trees to make it prettier - except that some of those bushes suddenly come to life and eat you if you get too close, and some of the trees wake up and shake their branches to incite the bees in a beehive to sting you. The only way to recognize bad trees from harmless ones is the presence of the beehive - no such luck with the bushes, meaning your best strategy is to torch every last one you see, just in case.
- Phantos from Super Mario Bros. 2. They look pretty much like background scenery until you pick up a key... and then they chase you through the entire level until you use said key on a door. There is also the final hawk-head doorway, which attacks your character when you pick up the crystal that otherwise opens its earlier counterparts in the game.
- There's the sun in two levels of Super Mario Bros. 3. First you think "Why the heck does the sun have a FACE?" Then it tries to kill you.
- The various defunct robots in the Wrecked Ship segment of Super Metroid come to life and attack your character when the power come back up.
- You know those Chozo statues that Samus gets stuff from? Two of them try to kill you at different points in the game.
- Tower Of Heaven eventually does this with the living things due to its book of laws.
- There are lots of monsters like this in Xenoblade Chronicles X. They tend to be completely indistinguishable from the bits of scenery they're disguising themselves as, and can't be targeted directly until they've revealed themselves, nor do they show on your radar. This can occasionally lead to you getting into a bigger fight then intended if an area effect attack happens to hit some hidden monsters accidentally.
- While they don't disguise themselves, some of the robots and mechs utilized by Ganglion can be encountered in an inactive, untargetable state, only for them to suddenly spring to life and attack when approached. One will quickly learn that just because it looks broken doesn't mean that it necessarily is...
- Ys has a chest in Darm Tower surrounded by statues that become Demonic Spiders once you take the treasure.