At the end of the turn, Golden Flowers will add a base copy of all ally cards destroyed this turn to your hand as long as the flowers are still on the field. This will continue every turn as long as the flowers are on the field. These replicas will have their normal base stats without any buffs or other status changes. This is akin to Resurrection, and a reference to Chara being buried under Golden Flowers before resurrecting.
Monsters that are brought back via this method will still be in the 'graveyard' and so can be brought back by Resurrection. If you don't have enough spaces in your hand, cards will return to your hand based on the order they died in (first to last) and the ones not resurrected will remain in the graveyard.
Best used in combination with Legendary cards, taunts or cards that can summon other cards, such as Temmie or So Sorry. If used in tandem with cards such as Flowey or Frisk, it's possible to duplicate them for each time they die as you are only receiving a copy of the card instead of removing it from the graveyard. Having two at once can be devastating, as it will give two of the same card back and revive each other, though it takes up spaces which could be used to play the cards.