Make sure to play Mirei Mikagura in the opening turns.
This set's [EX6-020 Gatomon] has an On Play/When Digivolving effect that makes it easier to prepare cards that lead to Mastemon. When used correctly, [EX6-022 Angewomon] and [EX6-053 LadyDevimon] can also make it easier to play Mirei Mikagura cards.
When you get to the mid-point of the game, DNA digivolve your Digimon into Mastemon, play Angel Digimon into the battle area, and try to remove your opponent's cards so you can emerge victorious.
If you can master [EX6-029 Mastemon ACE]'s <Blast DNA Digivolve>, you can play cards and remove your opponent's cards even during their turn, giving you extra defensive abilities.
The tactician Mastemon is perfect for a wide variety of situations to give you the upper hand against your opponent!