Dark Hole chain 1--> Formula chain 2 = Trishula synchro-summoned --> back to Dark Hole effect, Trishula is destroyed.
After dark hole effect --> Trishula resolves in grave since it was synchro-summoned successfully.
When this card is Synchro Summoned, you can activate this effect
to remove from play up to one card each from your opponent's hand, field and Graveyard. (The card in the hand is chosen at random.)
From my point of view.