"Trap Monsters" are a group of Trap Cards that Special Summon themselves as a Monster Card by their own effects. In some cases, once the monster has been Summoned, it is both a monster and a Trap Card simultaneously, and in other cases, the Trap Card will simply Special Summon itself as solely a monster card. The card's text will state which is the case. Examples of these kinds of cards include "Zoma the Spirit" and "The Prime Monarch".
Still a Trap Card
Identified by card text: (This card is also still a Trap.)
Trap Monsters are Special Summoned to the field from the Spell & Trap Zone when they resolve, and are subsequently treated as both Monster Cards and Trap Cards. Prior to the Master Rules April 1st 2020 Revision, they took up both a Monster Zone and a Spell & Trap Zone at the same time.
These Trap Monsters are affected both by effects that affect monsters, such as "Dark Hole", and affects that affect Trap Cards, such as "Harpie's Feather Duster", and can be targeted as either a Monster Card or as a Trap Card.
If they are negated with "Jinzo" or "Royal Decree", they will return to the Spell & Trap Zone as Continuous Trap Cards with no effect, and will remain there even after "Jinzo" or "Royal Decree" are removed. If "Book of Moon" is used on an already active Trap Monster, the Trap Monster is Set as a Trap Card again and can be activated and Special Summoned the next turn. If there are no available Spell & Trap Zones for the Trap Monster to be Set in when this occurs, then the Trap Monster will be sent to the Graveyard via game mechanics.
If a card or effect that destroys monsters specifically (like "Mirror Force") is activated, cards like "My Body as a Shield" can be activated to protect a Trap Monster, whereas cards like "Fake Trap" cannot be; likewise, if a card or effect that destroys Trap cards specifically (like "Heavy Storm") is activated, cards like "Fake Trap" can be activated, whereas cards like "My Body as a Shield" cannot. If a card or effect which can destroy both monsters and Traps (like "Raigeki Break") is activated, then both cards like "My Body as a Shield" and "Fake Trap" can be activated. In all cases, effects like that of "Imperial Custom" prevent Trap Monsters from being destroyed, even by battle.
Not a Trap Card
Identified by card text: (This card is NOT treated as a Trap.)
Some Trap Cards also have effects which Special Summon themselves as a monster that is not also treated as a Trap Card, most often a secondary one that activates from the Graveyard. Once the effect resolves, and the Trap Card is Special Summoned as a monster, it does not also occupy a Spell & Trap Zone, and functions exactly like a regular Monster Card.
If one of these monsters is flipped face-down, it is Set in the Monster Zone. If flipped face-up again after that, it will still be a monster. However, in this case, conditions that specify "If Summoned this way" will not be applied anymore.
Trap Monsters are typically used as an emergency defense to stonewall an opponent ("Metal Reflect Slime" is particularly useful in this regard). They can also used to provide quick Tribute fodder ("Metal Reflect Slime" is great when combined with "Level Eater"), such as the Monarchs, and can in some cases be used offensively as well. Also, because they don't count as monsters while in a player's Deck or Graveyard, some effects might work on them as a Trap Card, while others (like the effect of "Morphing Jar #2") don't see them as a monster. This can be helpful in some cases (see All-Out Attacks OTK).
Another use for Trap Monsters is for Synchro Summoning or Xyz Summoning. Since most Trap Monsters are Level 4, they can be used to quickly Synchro Summon a Level 5-8 monster or Xyz Summon a Rank 4 monster. "Metal Reflect Slime", which is too high a level to be useful for a Synchro Summon, can be used for Rank 10 Monsters such as "Superdreadnought Rail Cannon Gustav Max". If combined with a Level 1 Tuner monster, they can be also used to Synchro Summon "Star Eater". "Shapesister" is a Level 2 Tuner Trap Monster that can be used to assist in Synchro Summoning.
"Imperial Custom" makes Continuous Trap Cards indestructible. If you control a copy of "Imperial Custom" and a Trap Monster that is still treated as a Trap Card, the Trap Monster will not be able to be destroyed by battle or by a card effect. This combination is especially potent in defensive decks.
It is usually a good idea to have "Trap Eater" and "Double Snare" and "Splendid Venus" in the Side Deck of a Deck using high concentrations of these cards, so that you can remove cards such as "Royal Decree" and "Jinzo" which obstruct the use of Trap Monsters. "Magic Planter" is also useful, allowing the player to send Trap Monsters to the Graveyard to draw cards; this is particularly useful if the Trap Monsters have their effects negated, which causes them to remain on the field as Continuous Trap Cards only.
List of Trap Monsters
|D/D Cold Golem||???||???||???||1||300||???|
|D/D Greedy Golem||???||???||???||???||?||???|
|Death Spirit Zoma||???||???||???||???||1800||500|
|Embodiment of Apophis||Normal Monster||Reptile||EARTH||4||1600||1800|
|Metal Reflect Slime||Normal Monster||???||???||???||0||?|
|Phantom Knights Dark Gauntlet||Effect Monster||???||???||4||?||600|
|Phantom Knights Shade Brigandine||???||???||???||4||?||800|
|Stronghold the Moving Fortress||Effect Monster||Machine||EARTH||4||0||2000|