DCGO/Assets/Scripts/CardEffectCommons/MinMax_DP_Cost_Level/Cost/IsMinCost.cs

using System;
using System.Linq;

public partial class CardEffectCommons
{
    public static bool IsMinCost(Permanent permanent, Player owner, bool IsDigimonOnly, Func<Permanent, bool> condition = null)
    {
        if (permanent == null) return false;
        if (permanent.TopCard == null) return false;
        if (permanent.TopCard.Owner != owner) return false;
        if (!IsPermanentExistsOnOwnerBattleArea(permanent, permanent.TopCard)) return false;
        if (!permanent.IsDigimon && !permanent.IsTamer) return false;
        if (condition != null && !condition(permanent)) return false;
        if (!permanent.TopCard.HasPlayCost) return false;

        if (IsDigimonOnly)
        {
            if (!permanent.IsDigimon) return false;
            var costs = permanent.TopCard.Owner.GetBattleAreaDigimons()
                .Filter(x => x.TopCard.HasPlayCost)
                .Select(x => x.TopCard.GetCostItself).ToList();

            return costs.Count >= 1 && permanent.TopCard.GetCostItself == costs.Min();
        }
        else
        {
            var costs = permanent.TopCard.Owner.GetBattleAreaPermanents()
                 .Filter(x => (x.IsDigimon || x.IsTamer) && x.TopCard.HasPlayCost)
                 .Select(x => x.TopCard.GetCostItself).ToList();
            return costs.Count >= 1 && permanent.TopCard.GetCostItself == costs.Min();
        }
    }
}