Conventional encryption solutions cannot defend against a coercive attacker who can capture the device owner, and force the owner to disclose keys used for decrypting sensitive data. To defend against such a coercive adversary, Plausibly Deniable Encryption (PDE) was introduced to allow the device owner to deny the very existence of sensitive data. The existing PDE systems built for computing devices equipped with flash storage media, are problematic, since they cannot defend against multi-snapshot adversaries, who may have access to the storage medium of a user's device at different points of time. In this article, we propose MDEFTL, a secure multi-snapshot PDE system for mobile devices which incorporates plausible deniability into Flash Translation Layer (FTL). MDEFTL is the first practical design which integrates multi-snapshot PDE into FTL, a pervasively deployed layer in literally all the current mobile devices. A salient advantage of MDEFTL lies in its capability of achieving multi-snapshot plausible deniability while being able to accommodate the special nature of NAND flash as well as eliminate deniability compromises from it. We implemented MDEFTL using an open-source NAND flash controller. The experimental results show that, compared to conventional encryption which does not provide deniability, our MDEFTL only incurs a small overhead.