in this event just focus on getting whole set including Mythic Toy. As there is no ranking, so there is even less pressure and you can surely target to get Toys only (it will be a good boost for your deck).
Treat this latest Pussy Market event as test run. I think developer is considering how to reward this event (as toys only reward is silly when you can get all from Market shop and there is not benefit of getting double), so in future this event is bound to change.
Just use keys you get as reward from Colosseum (as last option) - in case you are not lucky enough to get atleast one Epic, Mythic or Legendary chest from Colosseum Fight (they do count as Tower chest - BUT it was buggy for me in one event and I has bad experience with this) OR from Tower chests.
For new players or players at low levels - Save gems and use it specifically for Epic chest and in case you are not good enough to get key item from Colosseum event (I think you need 168 for Epic chest - so basically 3 or 4 level up which is easier at low level than at high player level) - also this is usually the first real block for your progress in event goals. (Do not waste your gems for gold/rare chests)
