Once Bristlepack Sentry has legally attacked, causing its last ability to not apply by removing other creatures from the battlefield or reducing the power of one or more creatures won't cause Bristlepack Sentry to stop attacking
The materials needed are listed on the first line of the card, so pay attention to that when performing the Summon
However, while this effect wouldn't draw much attention to itself in most game, Yu-Gi-Oh's implementation has been banned for over 15 years, and many far more restrictive versions have filled the gap
Teferi, Temporal Archmage Theres a competitive EDH deck out there that essentially goes infinite with Teferi, Temporal Archmage, The Chain Veil, and a couple mana rocks
Additionally, its good to know about the repacks