Spindash (untested)

// Spindash

// CombatConfig.cs
    public class Combat
    {
    .
    .
    .
        public const int SPINDASH_ATK_SPD = 6; // change here if it needs to be edited
    .
    .
    .
    }

// Game_Unit_Skill.cs
        internal void dmg_skill(
            ref int skill_dmg, ref int weapon_dmg, ref int actor_dmg, ref int support_dmg,
            ref int target_def, Data_Weapon weapon,
            Game_Unit target, Data_Weapon target_weapon, WeaponTriangle tri, bool magic,
            int? distance, float effectiveness = 1)
        {
        .
        .
        .
            // Skill: Spindash
            if (target != null)
                if (actor.has_skill("SPINDASH") && Temp_Moved >= 1 && Global.game_state.team_turn == team)
                    skill_dmg += Temp_Moved;
        }

// New function
// placed under is_brave_blocked()
        public bool is_brave(Game_Unit target)
        {
            bool bravery = false;
            // Skills: Spindash
            if (target != null)
            {
                int speedmult = actor.atk_spd(distance) - target.atk_spd(distance);
                if ((actor.has_skill("SPINDASH") && speedmult >= Constants.Combat.SPINDASH_ATK_SPD && Global.game_state.team_turn == team)
                    bravery = true;
            }
            return bravery;
        }

// Multiplier_Img.cs
        public int get_multi(Game_Unit unit, Combat_Map_Object target, TactileLibrary.Data_Weapon weapon, int distance)
        {
            int multi = 0;
            if (!target.is_unit())
                return 0;
            if ((weapon.Brave() || unit.is_brave(target as Game_Unit)) && !unit.is_brave_blocked()) // <-- the new line
                multi += 4;
            if (unit.can_double_attack(target, distance))
                multi += 2;
            return multi / 2;
        }

// Combat_Data.cs
        private void add_attacks(
            Game_Unit battler_1, Combat_Map_Object battler_2,
            int i, Data_Weapon weapon)
        {
#if DEBUG
            System.Diagnostics.Debug.Assert(i == 1 || i == 2);
#endif
            Game_Unit attacker = i == 2 ? battler_2 as Game_Unit : battler_1;
            Combat_Map_Object target = i == 2 ? battler_1 : battler_2;

            int num_hits = 1;
            if (!attacker.is_brave_blocked())
            {
                // If only single hits against terrain
                if (!(target != null && !target.is_unit() &&
                        Constants.Combat.BRAVE_BLOCKED_AGAINST_DESTROYABLE))
                    num_hits = weapon.HitsPerAttack;
                if (num_hits == 1)
                    if (attacker.is_brave(target as Game_Unit)) // <-- new line
                        num_hits = 2;
            }
            for (int j = 0; j < num_hits; j++)
                add_attacks(battler_1, battler_2, i);
        }

// Game_Unit.cs
        private int attacks_per_round(int spd, Combat_Map_Object target, int distance)
        {
            if (target.is_unit() && !is_double_disabled())
                if (!stop_follow_up_modifiers(target as Game_Unit) && !(target as Game_Unit).stop_follow_up_modifiers(this))
                {
                    int target_spd = (target as Game_Unit).atk_spd(distance);
                    // If Spin Dash active, drop attacks per round to 1, make exception for brave weapons? idk
                    if (this.is_brave(target as Game_Unit))
                        return 1;
                    // If enough faster than the opponent, attack twice
                    if (spd - Constants.Combat.DBL_ATK_SPD >= target_spd)
                        return 2;
                }
            return 1;
        }