The ability for effects that Obliterate to destroy equipment makes a lot of sense when you remember what it is the Darkin seek: Something that can obliterate their weapons and grant them Cessation of Existence
Upon summoning Rumble, you have the option to discard up to 3 cards, each giving him a specific keyword (Quick Attack, Spellshield and Impact). He's essentially disassembling the discarted cards and using the spare parts to upgrade his mech.
