Mega Dewgong retains its water and ice typing in this mega evolution, but gains the ability Synchronize, which passes on burns, poison and paralysis to one opposing Pokémon, assuming it does not have an immunity to the status effect. This ability is common in psychic Pokémon, and the addition of the pearl-like orbs all over Dewgong certainly makes one wonder if Mega Dewgong is more Sp. Attack oriented.
However, would hefting around those pearls slow Mega Dewgong down? I cannot say the design is entirely practical, though Pokémon generally do not mega evolve without the help of a trainer, so I do not think it would be an issue in the wild.