"Umbral Horror Ghoul" and "Umbral Horror Unform" with Vector
"Umbral Horror", known as "Umbral" (アンブラル Anburaru) in Japan, is an archetype used by Vector in the Yu-Gi-Oh! ZEXAL anime. It's composed mostly of weak DARK Fiend-Type monsters who revolve around Special Summoning other "Umbral Horror" monsters for quick Xyz Summons.
"Umbral Horrors" have unique abilities to quickly swarm the field to allow for quick Xyz Summons. Their DEF at 0 also make them an ideal target for cards such as "Masked Chameleon", "Druise the Duplicitous Druid" and "Debris Dragon", that can revive most of them from the Graveyard at the expense of having their effects negated. However this can also allow for successive and constant Summons of Rank 4 Xyz monsters and Level 5 or Level 8 Synchros, thus being capable of Summoning powerful monsters with ease. "Recurring Nightmare" can be used with the "Umbral Horror" monsters, principally "Umbral Horror Ghoul" or "Drewes and another "Umbral Horror" for an instant Rank 4 monster. Cards such as "Allure of Darkness" can be used easily for draw power. Furthermore considering the 0 ATK nature of "Umbral Horrors", including "Ghoul" through its own effect, "Reptilianne Vaskii" can be Summoned with ease, allowing potent field control through its effect.
Because of their effective ways to Summon Rank 4 monsters, one can afford Rank-Up plays with the Deck. Also if one uses the effect of "Umbral Horror Unform", it is entirely possible to Xyz Summon a Rank 4 that requires 3 materials with relative ease, and through Rank-Up one can easily Summon powerhouses such as "Utopia Ray V", "Number 104: Masquerade" and its evolved form "Number C104: Umbral Horror Masquerade" and also "Number 105: Battlin' Boxer Star Cestus" and "Number C105: Battlin' Boxer Comet Cestus" for massive field control and brutal damage potential.
As explained above, "Umbral Horrors" have low ATK and DEF, rendering them quite weak by themselves and thus likely to be destroyed. Furthermore effects such as that of "Umbral Horror Unform" needs it to ram itself into an opponent's monster, thus likely causing a substantial damage to one's Life Points. Most of the external support such as "Masked Chameleon", "Drewes", "Debris Dragon", and "Recurring Nightmare" focus exclusively on the Graveyard; therefore, cards that block the Graveyard such as "Necrovalley", "Macro Cosmos", or "Dimensional Fissure" can be downright fatal to the Deck. All "Umbral Horror" monsters and "Drewes" are DARK, so cards such as "Shadow-Imprisoning Mirror" can block all of those monsters, leaving few options available. Cards that prevent effects such as "Skill Drain" can easily block "Masked Chameleon", "Drewes", and "Debris", thus preventing any revival plays from those monsters. "Chain Disappearance" can annihilate most "Umbral Horrors" and render them useless through banishing. "Doom Donuts" can also be used against "Umbral Horrors", although it is more of a short-term annoyance rather than a definitive threat.