What's wrong with AncientGreymon and why is there no winning record for this card?
This is perhaps the question many of us are asking. Even with promo [P-029] Agunimon being introduced, there is still no winning build for this combo.
I have played and tried out many different strategies with AncientGreymon lately (in the BT6 meta) and in my opinion, the only way to win with this deck is by OTK (one turn kill).
The strategy is not to warp digivolution from [P-029] Agunimon to AncientGreymon, but building a normal digivolution chain from LV2 digitama to LV5 [BT4-015] Volcdramon or [BT4-016] Aldamon in raising area. I will move out only when I have at least a red tamer Yagami Taichi in the field to secure 3 memories when starting of the turn and add 1 more "Security Attack" for AncientGreymon.
With Agunimon's inheritable effect, we will only pay 3 memories when digivolving your LV5 into AncientGreymon ( it is only applied when you digivolve to AncientGreymon in the battle area). The digivolution chain (above image) with Tamer Yagami Taichi allows AncientGreymon a 5-security check with "Piercing" at 15000DP (the digitama [BT1-002] Babydmon gives +2000 DP if this digimon has "piercing", while the LV3 [BT6-010] Flamemon grants this digimon "piercing").
After we wipe out the opponent's security stack with AncientGreymon's attack, we need a final push to win the game. In this situation, if opponent has a blocker and if we have [BT5-086] Omegamon (to attack with "advance") in hand and at least 2 memory to digivolve a red tamer into [BT4-011] Agunimon, then we can win the game.
The option card [BT4-100] Trident Revolver is a very good option card for Agunimon deck. It can delete 1 opponent's digimon with 6000DP (LV4 blocker) or less and then we can play a tamer card that have play cost 4 or less from hand for free. I also add 1 copies of [BT4-017] RizeGreymon to play a red tamer for free when we trigger "Digiburst 2".
Because we can summon Tamer for free when we play Trident Revolver option card, 2 copies of [BT1-084] Yagami Taichi and 2 copies of [BT4-092] Marcus Daimon are included for this deck, it increases the chance to draw tamer. Marcus Daimon can help to gain 1 memory when AncientGreymon declares attack, and if we have enough memory, this tamer can be used to digivolve to LV4 Agunimon and perform one security attack (when this tamer is not suspended).
I put 1 copies of [P-024] "Tai, You have grown up" to draw 3, it sometimes saves me when I have bad hand draw. [BT3-097] "A Delicate Plan" option card, with only 1 cost to play, it can help to prevent any option-threat that reveals from opponent's security check, I put 2 copies of A Delicate Plan into this deck.
Playing this deck, I always calculate carefully so that the security stack does not run out before I can attack our opponent with OTK.
Reserve more memories with "delay" option card, try to play more tamers, building the digivolution chain for AncientGreymon in raising area and only move out when we have enough option to win the game in one turn.
Deck profile is uploaded below, I made a changed to use Rowdy Rocker instead of Tai, You have grown up for draw power. Actually I want to use 3 copies of Tai Kamiya tamer and 1 copy of Marcus Daimon, but we only have 2 cards of Tai tamer, that's why.