Unless stated otherwise, everything here is Diablo II: Resurrected build 3.3.93847, Reign of the Warlock.
Unless stated otherwise, everything here is Diablo II: Resurrected build 3.3.93847, Reign of the Warlock.

When two weapons are equipped attacks two targets if possible, or one target twice.
Double Swing is a Barbarian Combat Skill (level 6, requires Bash; it unlocks Double Throw). It needs a melee weapon in each hand (skills.txt itypea1 and itypeb1 are both "mele") and swings both in one sequence: two targets if two are in reach, otherwise the same target twice. Its own level buys attack rating and a falling mana cost; its damage bonus comes entirely from hard points in Bash.
| Level | Mana | Attack Rating: + |
|---|---|---|
| 1 | 1 | 15% |
| 2 | 0.88 | 20% |
| 3 | 0.75 | 25% |
| 4 | 0.63 | 30% |
| 5 | 0.50 | 35% |
| 6 | 0.38 | 40% |
| 7 | 0.25 | 45% |
| 8 | 0.13 | 50% |
| 9 | 0 | 55% |
| 10 | 0 | 60% |
| 11 | 0 | 65% |
| 12 | 0 | 70% |
| 13 | 0 | 75% |
| 14 | 0 | 80% |
| 15 | 0 | 85% |
| 16 | 0 | 90% |
| 17 | 0 | 95% |
| 18 | 0 | 100% |
| 19 | 0 | 105% |
| 20 | 0 | 110% |
| 21 | 0 | 115% |
| 22 | 0 | 120% |
| 23 | 0 | 125% |
| 24 | 0 | 130% |
| 25 | 0 | 135% |
| 26 | 0 | 140% |
| 27 | 0 | 145% |
| 28 | 0 | 150% |
| 29 | 0 | 155% |
| 30 | 0 | 160% |
The attack-rating bonus is ToHit 15 plus LevToHit 5 a level: +15% at level 1, +110% at level 20, +160% at level 30, and it counts +skills. The tooltip's damage line is 10 × Bash hard points (calc1 reads skill('Bash'.blvl) × Param8) and nothing else, so it is left out of the table: it is 0 at every level of Double Swing without Bash points, and +200% at every level with 20.
Mana is the odd one: the row's mana is 8 in 32nds (manashift 5), so 1 mana at level 1, and lvlmana is −1, so each level takes 1/32 off (0.875 at level 2, 0.5 at level 5) until it is 0 from level 9. The column above is the cost per weapon; the Basin's page says the cost is charged once for each weapon in the sequence, so the tooltip prints double (2 at level 1), and the skill can still be started with 1 mana.
The row also carries a 50 under "Attack rate bonus" (Param1) and "Attack Speed %" (Param5, calc3); the tooltip does not print it.
Each swing is a normal weapon attack: it rolls Chance to Hit with its own weapon's attack rating plus Double Swing's bonus, and deals that weapon's physical damage with the Bash synergy added to your other Enhanced Damage. Everything a weapon hit carries, leech, Crushing Blow, Deadly Strike, Open Wounds, applies to each swing with the weapon that made it. If no target is selected, the Basin says targets in range are picked automatically.
There is no bonus damage of Double Swing's own. At 0 hard points in Bash a level 20 Double Swing hits for plain weapon damage with +110% attack rating; its value is the second swing and the price.
The synergy reads blvl; the attack-rating and mana lines read lvl, so +skills from items raise the attack rating and finish paying the mana down but add no damage. Double Swing feeds Double Throw (+8% damage per hard point) and Frenzy (+8% damage per hard point). A weapon mastery adds its attack rating, damage and critical-hit chance to each swing with a weapon of its class, so two different weapons can draw on two masteries.
A player's hit on another player is cut to 17% of its value (difficultylevels.txt PlayerDamagePercentVSPlayer) before anything else, see Player versus Player. Both swings are cut the same way; nothing else about Double Swing changes.
Written from the game's tables (build 3.3.93847) and the cited pages; a per-level table is computed from skills.txt and skilldesc.txt by the same evaluator the skill pages use. A “legacy rule” is a published engine rule no table proves; a “game table” is read from the table named. · Report incorrect data