Rather than trying to go second, pray your opponent Xyz summons, and rely on a continuous spell effect to get two normal summons before you can Xyz summon, I've made the pro gamer decision to simply not play this deck pure. Instead, I opted to run it alongside the easiest level 3 engine I know, Neiroy the Traitor. He gets 2 free lvl 3s to start Xyzing. I know Dream Mirror needs a big package to operate, but if you need more Goblin Bikers, you can probably cut 1 Mara and 1 Sprite. Sprite can search any DM card from your deck, so the fusion spell at 1 is just fine. But if it gets negated, Oneiros is up a creek, so a second may be a good idea. Absolutely keep Foe so Friend can swap out with him and start burning opponent with Mirror of Terror.
After further examination, I realized Goblin Bikers are such a consistent engine that you only need 1 of each, including the search spell. You just have to play the archetype in reverse. All it takes is resolving both Neiroys' summons. You don't even need to use Traitor's second effect, but if you do, tribute Disciple to add Joy and ss Friend, who will resurrect Disciple. Xyz Big Gabonga, which searches Dugg, which searches Grand Entrance, which searches another Biker. THEN you Xyz Gold Pride Chariot Carrie with the 2 new Bikers. She's just net positive, and all it takes is 2 lvl 3s. Chariot gets you Better Luck Next Time, which gets you Captain Carrie, which gets you Neck and Neck, which returns a GP monster you control or card in your gy to your hand. Chariot will have 1 material left over for you to banish Grand Entrance to add back a Biker from the gy to your hand. During the end phase, you shuffle Chariot to draw 1 and attach a remaining Biker from the deck to Gabonga. Ultimate PROFIT.
If you can't afford the minuscule GP package, use Fortune Tune instead. You can devote more of its material toward Bikers, and it recycles itself and Neiroys when leaving the field. I like Stampede as a second search target for Dug when resurrected. It lets you potentially Xyz monster negates like Ashura King and Tri-Edge Levia on your opponent's turn. You can also just use the 2 Biker quick effects to fuel Masquerena.
The Bikers can use any Goblin monster, so I got Goblin of Greed as an anti-handtrap. Assuming you make it that far before being nuked by them. Better than no answer, right?
Okay, so Crazy Beast IS out, but the damn thing wouldn't show up when I searched TCGPlayer. Grialle Trio isn't, so it's in the side deck. Grand Meeting allows 2 GBs to become lvl 6, but it still dilutes the engine, and the lackluster extra ns is better used in a purer Biker deck. I do want Crazy Beast, so I might find room for it in here after testing. Nope, doesn't fit. They are bricks. Maybe next trap.