From the official Japanese Twitter account.

Were Garurumon

Card NumberBT1-040Level5
Card TypeDigimonPlay Cost6
ColorBlueEvolution Cost3
Digimon TypeBeast ManDP7000
AttributeVaccineRarityUncommon
StagePerfectArtistsasasi
Main Effect[When it attacks] Memory +3. At the end of this turn, Memory -3.
Source Effect

This effect appears to be designed with the new Tamer Cards in mind, which ensure the opponent will always have at least 3 Memory on their turn. These new cards allow you to play around that a bit, gaining extra Memory that allows you to play more cards and ideally manipulate the gauge so that it ends exactly on the opponent’s 1. That 1 Memory then jumps up to 4 thanks to these effects—the opponent ends up with 1 more Memory than if their Tamer Card had resolved, but you get to have 3 more Memory during your turn, a positive exchange for you.

Metal Greymon

Card NumberBT1-021Level5
Card TypeDigimonPlay Cost6
ColorRedEvolution Cost3
Digimon TypeCyborgDP7000
AttributeVaccineRarityUncommon
StagePerfectArtistTANIMESO
Main Effect[When it attacks] Memory +3. At the end of this turn, Memory -3.
Source Effect

Booster 1 launches in Japan May 15th, 2020.