On the twitter page of the Mana series, they posted a video showing two people who appear to be playing Seiken Densetsu 3 (also known as Secret of Mana 2 to fans) which is the follow up successor to Secret of Mana for the SNES. The people behind the mana series are preparing for a 25th anniversary, so this could be one of their surprises besides the 25th anniversary concert of the Seiken Densetsu series as a whole.

Source Article:
Mana series Twitter account posts 10-second video of Seiken Densetsu 3 running on Switch - Gematsu

Here's their twitter page
-- (@Seiken_PR) on Twitter