I won more than one old Vintage tournament that way with nothing in my deck more expensive than Jester's Cap, thanks to turn after turn of card advantage
Barian's Seal Card Text When your opponent activates a Spell/Trap Card, or monster effect, while you control a "CXyz" monster or a "Number C" monster with a number between "101" and "107" in its name: Negate the activation, then you can attach 1 monster from either field or GY to 1 Xyz Monster you control
The main attraction here is that you can pay two mana to search your library for a Dragon and then have Scion turn into it for the rest of the turn
Because Im normally getting two Altaria in play by turn 2, my Garchomp- EX can swing for 180 damage with a Muscle Band attached
You get an extra vamp token for every vampire you cast (even while it's in the command zone), consistent and recurring +1/+1 counters for all your bloodsucking minions, and the card itself has first strike and haste