Introduction and History
Ever since the release of Pendulum Evolution in 2017, Pendulum Magicians have constantly evolved to adapt to the meta. The archetype had a slow start; Zoodiacs rampaged the meta and Magicians barely saw play. However, when Jeff Jones took a UDS after the next banlist, its popularity jumped and has seen play since.
Later, Master Rule 4 and the banlist forced the deck to adapt with the newly available tools. With Performapal Skullcrobat Joker forbidden, the next best normal summon became Supreme King Dragon Darkwurm. The inclusion of this dragon also made Dragon Shrine a pendulum staple. Now with Savage Strike and Duel Power dragon support, Darkwurm became the best current main decked pendulum next to Harmonizing Magician. Pendulum Guardragon is the current strategy to compete with the meta.
Main Deck Monsters
Spellcasters
The deck consists of a long list of monsters. First, we have the faithful Pendulum Magician lineup: Purple Poison Magician, Black Fang Magician, Oafdragon Magician, Wisdom-Eye Magician, and Harmonizing Magician. All perform as pendulum scales but are useful as monsters too. They are also all searchable by Pendulum Call. Harmonizing is incredible because it summons any Magician from the deck when pendulum summoned, making it a 1 card extra deck play.
The deck also play Chronograph Sorcerer and 1 copy of Timegazer Magician. They are a bit different from the rest of the Magicians because their best use is to turbo out Heavymetalfoes Electrumite.
The Mythical Beast engine is encouraged to add consistency to summoning Electrumite. Mythical Beast Master Cerberus is a great card going 2nd, as it can banish a monster. Mythical Beast Jackal King can negate any monster handtrap that disrupts Electrumite.
Dragons
After Joker's ban, Darkwurm has been filling the void within pendulum players' hearts. However, the introduction of Guardragons made Darkwurm an essential combo piece. As an easily accessible level 4 Dragon, it makes the Guardragon variant consistent and strong. Luster Pendulum, the Dracoslayer is another level 4 Dragon that can also turn into Elpy.
Another dragon used is Destrudo the Lost Dragon's Frisson. Easily summonable by Guardragon Elpy, Destrudo acts as 2 materials for pendulum plays. It also is not bad to open as it can be pendulum summoned or discarded for Pendulum Call.
Dragon techs can be played for the Hieratic Link's 2nd effect. Aether, the Evil Empowering Dragon is a great card that can also be used going 2nd and Amorphage monsters are a popular option to lock out the Extra Deck.
Spells
Pendulum Call and Dragon Shrine are the best ways to get Darkwurm in the GY, making them staples to this strategy and Foolish Burial acts as another Dragon Shrine. Duelist Alliance can be played to search Pendulum Call if needed. Other staple spells like Pot of Desires and Called by the Grave are also appreciated.
The best part about pendulums is that most of the spells are your monsters. Ultimately, the most important spells are the pendulum scales.
Extra Deck
The crucial cards here are Heavymetalfoes Electrumite, Triple Burst Dragon, Guardragons Elpy and Agarpain, and Hieratic Seal of the Heavenly Spheres.
Electrumite and Triple Burst are the play starters. Electrumite sets up everything needed before the Guardragon combo, and Triple Burst provides an arrow for Elpy. Heavenly Spheres allows you to link off Agarpain and Elpy for an interruption, while also unlocking zones. The other 10 slots are up to player preference, and usually includes Odd-Eyes Vortex Dragon, Borreload Savage Dragon, and generic R4nks. A level 7 Synchro is also recommended for plays with Timegazer Magician or Destrudo.
The Minimal Combo
The board's goal is to get a level 4 dragon under Electrumite's right arrow, and at least 1 other monster. Easy right? Link Darkwurm or Luster Pendulum into Elpy in the same spot, then Link Electrumite and another monster into Triple Burst. Next, use Elpy to spit out any dragon then link that dragon and Triple Burst into Agarpain.
Then, activate Agarpain to summon any Dragon from the Extra Deck. This could be Odd-Eyes Vortex Dragon, Borrelsword Dragon, or anything. Finally, link the 2 Guardragons for Heavenly Spheres to complete your combo. This is the minimal Pendulum Guardragon combo, and is your "gameplan". Having any lv6 or lower monster allows a play with Destrudo, and a Harmonizing allows a Borreload Savage Dragon or R4nk play.
Conclusion
This covers the gist of Pendulum Magician Guardragon. Although not very meta defining, Pendulums is always a consistent strategy. If you haven't already, feel free to try the deck out. However, don't expect this particular build to last forever; banlists and new cards will continue to evolve the strategy in future formats.