Can 'Bottomless Trap Hole' stop a Synchro Summon? - Answers

Bottomless Trap Hole can be used against a Synchro Summoned monster with appropriate attack, but it's not accurate to say it 'stops' the summon. In game terms, the summon is completed successfully, and cards like Bottomless Trap Hole will be used in response to that successful summon. It means though that Synchro Monsters like Brionac may have already used their effects due to player Priority - if you want to avoid even that happening, you need to negate the summon instead, with a summon negation card.