"/Assault Mode" monsters are extremely powerful, but in order to be used effectively their user must have very good control over their own deck and be able to summon the desired Synchro Monster with ease. A deck that is too dedicated to supporting "Assault Mode Activate" may not support the Synchro Monster properly enough to be able to summon it quickly. On occasion, an "/Assault Mode" monster's effect may not be as desirable as the original ("Hyper Psychic Blaster/Assault Mode" does less damage with its effect, generally, than its original version's Piercing Damage, and "Red Dragon Archfiend/Assault Mode" has a severe drawback).
Depending on how you build it, this deck can be very fast and very quick to kill your opponent. Decks that work slowly or take a while to get started, like a Spellcaster Deck or Frog Deck are at risk of destruction.
A way to deal massive damage to your opponent's life points is to have your Synchro Monster of choice on the field. "Hyper Psychic Blaster" will deal the most damage but "Stardust Dragon" has the greatest chance of working. Attack with the Synchro Monster, then use "Assault Mode Activate". You can also chain "Assault Mode Activate" to a "Mirror Force" or "Dimensional Prison" to avoid the loss of your monster and maintain field advantage. Then, attack with the /Assault Mode Monster. Activate "Assault Overload" and inflict damage to both players equal to the /Assault Mode Monsters' level X 200. Then attack with your original Synchro Monster and if your opponent has a clear field or you used "Hyper Psychic Blaster/Assault Mode" then you will win.
Adding /Assault Mode support to your deck adds a new level of difficulty. Anti-Meta Decks will annihilate this deck. Always make sure to have a good side deck to deal with these decks. Also, because these decks are completely dependent on the use of "Assault Mode Activate" the deck can be shut down by "Prohibition" so make sure to have Spell and Trap removal cards such as "Dust Tornado" or "Mystical Space Typhoon".
Another /Assault Mode deck weakness is that if you draw an /Assault Mode monster it will waste your draw. A way to solve this problem is to use "Hand Destruction" or "Card Destruction", then use "Pot of Avarice" to return them to the deck, so make sure you have some of those cards in your deck. Also, your opponent must discard cards as well so there is an added bonus to running these cards.
The deck that "Doomkaiser Dragon" fits best into is one built around "Zombie World", allowing you to Special Summon monsters from either player's graveyard. Possible uses for these monsters include tribute fodder, such as for "Beast King Barbaros" and the ability to easily activate its field-clearing effect; Synchro Summons, if you revive Tuner monsters; or fodder for anything that needs large amounts of monsters on the field.
Another good card to add to your Extra Deck would be "Tempest Magician". Her special effect allows you to add Spell Counters to any monster by discarding any number of cards from your hand. This is a useful way to increase the ATK of "Arcanite" and Counters if it runs out.
Once "Stardust Dragon" is summoned it is important to Special Summon "Stardust Dragon/Assault Mode" quickly; thus, "Assault Beast" is used to support "Assault Mode Activate". Once the "Stardust/Assault" is out it is extremely difficult to remove from the field - its effect will negate ATK modifiers, destruction effects and more. The three weaknesses for this card are cards to negate "Stardust Dragon/Assault Mode's" effect, like "Divine Wrath", cards that banishes monsters from the graveyard, such as "D.D. Crow", and monsters that have ATK higher than or equal to 3000 without using an effect, such as "Beast Machine King Barbaros Ür".
To speed up this deck you might want to add "Foolish Burial" to send your "Destiny Hero - Malicious" graveyard in order to activate its effect, then summon "Arcane Apprentice". This way you can easily Special Summon "Stardust Dragon" and get an "Assault Mode Activate". "Mystic Tomato" can be useful too as it can summon "Destiny Hero - Malicious" from your deck. Add "Plaguespreader Zombie" to help you return your "Stardust Dragon/Assault Mode" or "Destiny Hero - Malicious" from your hand to your deck.
While relying on Malicious to Synchro Summon "Stardust Dragon" can be unreliable, using Flamvells to summon a Stardust can be surprisingly easy. Destroy one of your opponent's monsters with "Flamvell Firedog" (Level 4) and Special Summon "Flamvell Magician" (Level 4 tuner). Tune them together for a "Stardust Dragon". Also, once a sufficient amount of Flamvells have been added to your Graveyard, "Rekindling" is a quick and easy way to Synchro again for "Stardust Dragon".
This deck is based on tuning Level 8 Synchro Monsters using "Flamvell Magician" and "Flamvell Firedog". "Firedog" Special Summons "Magician" quickly with his Effect and they could tune to make a Level 8 Synchro Monster in Main Phase 2 after "Firedog's" Effect and the only thing you have to do is activate "Assault Mode Activate" as soon as you can. Also, you can activate "Rekindling" to return Flamvells and tune them again.
Strategy of this deck is simple and you just have to summon "Firedog" as quick as you can and blow away your opponent with Synchro Monsters and /Assault Mode Monsters.
This deck is based on tuning Level 4 non-Tuner Winged Beast-Type monsters with Level 2 Dragon-Type Tuner to summon "Dragunity Knight - Vajrayana". Special Summoning "Dragunity Arma Mystletainn" from hand can lead to summoning "Stardust Dragon". Strategy of this deck is simple and you just have to use "Dragon Ravine" as early as possible to spam Synchro Monsters and /Assault Mode Monsters.
This deck is quite possibly the easiest of the Assault Mode decks to use due to the usability of "Overdrive Teleporter" and "Hyper Psychic Blaster" being a Level 9 Synchro Monster. Thus, Special Summoning "Hyper Psychic Blaster" is as simple as Tribute Summoning "Overdrive Teleporter", Special Summoning at least one "Psychic Commander" and tuning "Teleporter" and "Commander" to Synchro Summon "Blaster". From there, activate "Assault Mode Activate" as soon as possible.
A notable feature of "Hyper Psychic Blaster" is the summoning condition. Unlike other Level 9 Synchro Monsters, such as "Mist Wurm" and "Trishula, Dragon of the Ice Barrier", "Hyper Psychic Blaster" only needs 1 other monster (at minimum) to Synchro Summon it. Most of these decks take advantage of this valuable fact as much as possible.
This build is centered around "Hieratics" and throwing out "Ultimaya" using "Labradorite Dragon" and going for "Stardust Dragon/Assault Mode" with setting "Assault Mode Activate". The Deck is fairly straight forward and easy to learn, and you have access to all of the other "Hieratic" staples. You also should run "Quickdraw Synchron" and "Magical Mallet" so you can shuffle "Stardust Dragon/Assault Mode" back to the Deck. It also helps against dead hands, which happens often in "Hieratics".
For getting "Ultimaya" out, you can run cards like "Cyber Dragon" and "Wattaildragon". Any Level 5 vanilla Dragon is also a option, but is not recommended. You can also run "Instant Fusion", but lowers the speed of the Deck. The Deck has access to all Level 7 & 8 Dragon Synchros, such as "Beelze of the Diabolic Dragons" and "Black Rose Moonlight Dragon".