A good opening barrage can keep the opponent off-kilter, especially if it's a slow deck
SE Secret Rare STAR Starlight Rare The Fabled Behilmoth X LIGHT Level 2 [ BeastTunerEffect ] ATK 1000 DEF 600 If this card is in your hand: You can discard 2 or more "Fabled" monsters, including this card, and if you do, Special Summon 1 "Fabled" Synchro Monster from your Extra Deck whose Level equals the discarded monsters' total original Levels (this is treated as a Synchro Summon)
You must control no Spells or Traps to activate and resolve this effect
Regardless of outcome the opponent gets to stack their Deck in any order (since you didn't say what happens to the remaining cards on a success, I presume the stack happens regardless of outcome), and nowadays a lot of Decks benefit off having monsters in the Graveyard, for better or worse
If youre trying to build a huge Army, youre going to be a little less interested in repeatable effects that let you amass, and more interested in cards that can give you an incredibly high Amass value