“X-Saber” is one of the few archetypes we have in Duel Links that is actually capable of Synchro Summoning: it doesn't have to go out of its way to Special Summon monsters from the Extra Deck, but, at the same time, it doesn't completely rely on them.
Since a lot of the new “Goyo” Synchro monsters that have just been introduced into the game benefit from having Warrior-Type EARTH monsters on their side of the field and they also have pretty generic requirements when it comes to materials, it's only normal to pair them with X-Sabers.
If your opponent controls a monster(s) and you control none, you can Special Summon this Level 1 Tuner from your hand. Unknown Synchron is a great card that gives you easy access to Level 5 Synchros such as X-Saber Wayne and Goyo Chaser, but it can also be used to Special Summon higher Level monsters from your Extra Deck (if you use Powerful Rebirth to Special Summon XX-Saber Boggart from the Graveyard, its Level is going to increase by 1, giving you access to the Level 6 XX-Saber Hyunlei and Goyo Predator).
XX-Saber Fulhelmknight is a Level 3 Tuner, it doesn’t Special Summon itself like Unknown Synchron, but, once while it’s face-up on the field, it allows you to negate an attack declared by an opponent’s monster.
You can use Fulhelmknight and XX-Boggart Knight to Synchro Summon X-Saber Souza or, if one of them was Special Summoned by Powerful Rebirth, even Stardust Dragon and Goyo King.
You can use Fulhelmknight and XX-Saber Darksoul to Synchro Summon XX-Saber Hyunlei, Goyo Predator, Goyo Guardian or X-Saber Souza.
You can use Fulhelmknight and Paleozoic Canadia to Special Summon Goyo Chaser, X-Saber Wayne or XX-Saber Hyunlei, Goyo Predator and Goyo Guardian.
When Normal Summoned, XX-Saber Boggart Knight allows you to Special Summon a Level 4 or lower “X - Saber” from your hand—this is your main way of swarming the field with this deck. Boggart Knight makes it easy to Synchro Summon and it also synergizes well with Saber Slash.
If XX-Saber Darksoul was sent from the field to the Graveyard, during the End Phase, you get to add a “X - Saber” monster from your Deck to your hand; this effect will activate even if you used Darksoul as Synchro Material, but not if the monster is banished.
Paleozoic Canadia is able to slow down decks such as Vampire and Masked HERO, but, thanks to its secondary effect, it can also be Special Summon as a Level 2 monster from the Graveyard and used as material for a Synchro Monster.
When X-Saber Wayne is Synchro Summoned, it allows you to Special Summon one of your “X-Saber” monsters from your hand, it is pretty low in terms of ATK, but, in combination with XX-Saber Boggart Knight, it can finish off the opponent.
There are a couple ways you can Synchro Summon this Level 9 monster: you can use three of your monsters, including Paleozoic Canadia, or you can take control of an opponent's Blue-Eyes White Dragon or Dragon Spirit of White and then use it, together with Unknown Synchron, to Special Summon this 3100+ ATK monster.
Goyo King is a Level 8 Synchro that, when declaring an attack, gains 400 ATK for each face-up Warrior-Type EARTH Synchro monster you control, including itself. When Goyo King destroys an opponent's monster by battle and sends it to the Graveyard, you can decide to Special Summon that monster or take control of another monster your opponent controls.
With 3200+ ATK on attack declaration, unless DNA Surgery or something else altered its Type or Attribute, Goyo King is capable of getting over Blue-Eyes White Dragon, Masked HERO Anki and even Cosmo Brain and then Special Summon them on your side of the field, ready attack.
A Level 6 Synchro with a similar effect to Goyo King, Goyo Guardian was locked behind a Skill with a pretty substantial drawback or a 40% chance. Goyo Guardian is undeniably a great card, it does lack enough ATK to get over some of the most common high ATK monsters you can find in PvP, but you can use Paleozoic Canadia to make up for it and just switch those monsters in the position in which they are more vulnerable.
Goyo Guardian, unlike Goyo King, Special Summons the monsters it destroyed by battle in Defense Position, making it impossible to use them right away for an attack without some outside help, and, when you take into consideration the limited Monster Card Zones we have in Duel Links, it really makes you wonder why the developers tried so hard to deter players from using this card.
Goyo Predator is essentially Goyo Guardian with no restriction on the Synchro Materials, but lower stats. The battle damage inflicted by the monsters Special Summoned by Goyo Predator's effect is halved, but you can Special Summon them in Attack Position and use the right away.
There isn't much to say about this Skill: you can end up with Goyo Guardian and Goyo King in your Extra Deck or with Goyo Chaser and Goyo Defender; each Synchro monster has a 40% chance of appearing in your Extra Deck, assuming the individual chance is the same for each one of them, which is likely, and there cannot be two copies of the same card.
If you build this deck NOT for competitive purpose, here is a little tip. For cheaper version, you can try using akiza's level up tuner. It's level can be adjusted, which is really good for this deck since the extra deck consist of various level. The problem is all your synchro monster must be EARTH, so you can't use something like stardust dragon. It will also be a bit slower.
Personally, I build this deck because I want a Trudge character deck that decent enough to be used against standard duelist.