If a monster on the field, with an ATK of 500 or less, is changed to Machine-Type with “DNA Surgery”, you can use “Machine Duplication” to Special Summon up to 2 copies of it from your Deck.
The Machine-Type monster is chosen at activation of this card, so if the opponent chains “Ring of Destruction” to destroy the chosen monster, up to 2 copies of that card can still be Special Summoned.