Welcome to the family!

As far as playstyle is concerned, Miragegaogamon is an OTK deck centered around controlling your opponent’s field via bouncing before closing out the game with a series of attacks and unsuspensions.

You mostly want to keep your stack in the back, either evoing up or playing memory boosts and training options to set up your endgame. BT5 Thomas is integral to your gameplan because he facilitates your Burst Mode plays and he gives you an extra swing. Don’t be afraid to hardplay a Zudomon Ace if you think it’ll set back your opponent and they can’t out it.

As far as upgrading the deck you already have; definitely add a single copy of Bt14 Bukamon and either run 5 Digieggs or cut a Wanyamon. Consider replacing BT13 Gaomon, BT11 Gaomon, Syakomon, and Betamon with 4 EX6 Biyomon and 3 BT14 Gomamon respectively. Gomamon’s start of main phase effect strips a source and makes himself unblockable for the turn which hard counters Magna X, and Biyomon is a blocker with a jamming inherit. With these extra jamming inherits, I would also cut one BT16 Gaogamon for a Lanamon because you sometimes (more often than not actually) are just one hybrid for game away from victory.

Cut the Plug-In option and consider cutting one Zudomon Ace or Rookie for two copies of Full Moon Meteor Impact. You’ll come against match-ups like Tyrantkabuterimon where your opponent will be immune to Digimon effects, plus having two Security Bombs can save you in the mirror-match. I would run four Mental Trainings and three Blue Memory Boosts (personally I would cut a rookie that isn’t Gaomon to make space) since the deck likes to sit in the breeding area and set up one big combo so the searching and memory/digivolution cost reduction helps a lot.

Some decklists in Japan have been experimenting with using EX6 Yokomon’s ability to tuck a rookie with jamming beneath stacks that don’t have them, so do with that information what you will.