History Main / SuddenlyHarmfulHarmlessObject

* ''VideoGame/{{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''.

* ''VideoGame/{{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.

* In ''VideoGame/DonkeyKongCountryReturns'', on Sunset Shores, the player is given a chance to enjoy the scenery before the DifficultySpike. Or at least it seems like it, until bushes uproot themselves & chase after you.
* ''VideoGame/{{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 [[AmbushingEnemy demonic hands]] appear from the previously much less terrifying water.

** Phantos from ''VideoGame/SuperMarioBros2''. They look like background scenery until you pick up a key... and then one of them chases 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 ''VideoGame/SuperMarioBros3''. First you think "Why the heck does the sun have a FACE?" Then it [[EverythingTryingToKillYou tries to kill you]].

* ''VideoGame/{{Ys}}'' has a chest in Darm Tower surrounded by statues that become DemonicSpiders once you take the treasure.

The Suddenly Harmful Harmless Object is a monster that is usually part of the scenery, or at least something benign, much like the WallMaster and ChestMonster. It becomes dangerous as soon as a [[EventFlag certain condition is met.]] Usually, they become harmless again the moment the condition is no longer met, although it's sometimes permanent.

** The water may also count. in 4-5 and later, the famous [[WallMaster demonic hands]] appear from the previously much less terrifying water.

[[folder:Hack and Slash]]

[[folder:Metroidvania]]
* ''VideoGame/CaveStory'' 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.
[[/folder]]

[[folder:Run and Gun]]
* ''VideoGame/{{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''.
[[/folder]]

[[folder:Survival Sandbox]]
* In ''VideoGame/DontStarve'' every time you chop down an evergreen, there's a minute chance a nearby one will transform into a hostile Treeguard.
[[/folder]]

* In ''VideoGame/AgeOfMythology'', 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.

* ''VideoGame/{{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 ''VideoGame/DontStarve'' every time you chop down an evergreen, there's a minute chance a nearby one will transform into a hostile Treeguard.
* Both ''VideoGame/DragonAgeOrigins'' and ''VideoGame/DragonAgeII'' have statues and suits of armor coming to life sometimes to attack the party.

* ''VideoGame/FinalFantasyIV'' 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. [[spoiler:In the same dungeon you end up fighting A WALL as its respective boss.]] After a dozen doors that's not a surprise even.
* ''VideoGame/KingdomRush'' series:
** The original game had the Pit of Fire stage where you see a sleeping [[HellHound Cerberus]] at one corner of the screen. It stays asleep until the final wave, after which it wakes up and attacks you as a MiniBoss-level enemy.
** ''Frontiers'' has the alien eggs in the Lost Jungle that start hatching out [[FaceHugger 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 [[MiniMecha MechaDwarf MK.9]] slowly marches out as the first GiantMook 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 ''VideoGame/TheLegendOfZeldaTheWindWaker''? Well, they turn into massive, spiked harbingers of death at times.
* In [[JungleJapes Sector 2 (TRO)]] of ''VideoGame/MetroidFusion'', 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.

* In ''VideoGame/PuzzleQuest 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 ''VideoGame/ResidentEvil''. 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 ''VideoGame/{{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.
* ''VideoGame/{{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.

* ''VideoGame/SuperMetroid'':
** The various defunct robots in the Wrecked Ship segment 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.