Cabal Stronghold You need at least five Swamps on the battlefield before Cabal Stronghold starts producing extra mana, and it just increases from there
The first thing to fix would be the character art
If you would draw a card while your library has no cards in it, instead return a creature card from your graveyard to the battlefield
Lower Text Link [TS] trait: Cost 3 (Plug this card from the hand or battle area sideways into the specified Digimon in the battle area.) [When Attacking] [Once Per Turn] Return 1 of your opponent's suspended Digimon to the hand
Considering they require two, three, and four Tuners respectively to Special Summon in the first place, this means at minimum they're dropping onto the field with 4500 ATK, 5500 ATK, and 6500 ATK respectively
This is a deck whose sum is greater than its parts, each piece combining to make some truly fearsome threats