What ability score does a Hexblade's Pact Weapon use for.
DC Bonus (Spells Only). Entering a number here will add to (or subtract from) your current calculated total. Offhand (Weapons Only). Checking this box will designate the weapon is an offhand weapon. This will typically mean that your ability modifier for the attack will no longer be added to damage. The feat Dual Wielder and the Two-Weapon.

Focusing on in-combat features, a Ranger-Paladin can use her bonus action to dual wield two light melee weapons. If she has already set her Hunter’s Mark on a target, and has unlocked Extra Attack at Ranger level 5, she can use her Hunter’s Mark bonus three times (Attack, Extra Attack, Bonus Action off-hand). Add in her Smite, and you’re looking at a powerful melee turn. Not to mention.

There's no offhand in 5e. You need 2 different light weapons (without Dual Wielder feat) to use TWF to get a bonus action attack. Per the improvised weapon rules, you could easily treat a rod as a club. So the warlock with haste could easily do this.

When you take the Attack action and attack with a light melee weapon that you're holding in one hand, you can use a bonus action to attack with a different light melee weapon that you're holding in the other hand. You don't add your ability modifier to the damage of the bonus attack, unless that modifier is negative. If either weapon has the thrown property, you can throw the weapon, instead.

Off-Hand Master. Prerequisites: Dexterity 13 or higher You are now able to make the most use of an offhand weapon, no matter the situation. You gain the following benefits. When you are wielding a separate melee weapon in each hand, and if you are able to use your bonus action to make an attack with this extra weapon, when you use your reaction to make an opportunity attack, you can make one.

Originally I would have thought it would have used the modifier for a XXX attack as a bonus action, because it isn't your off hand. However, I found that no such language as main hand or off hand are used in the rules, so I would say the bonus action would need to follow the rules of two weapon fighting and not gain the modifier, unless it is negative. I will be sure to include such language.

Assume I wield a Whip in one hand and a dagger in the other. If a creature moves from 5ft to 10ft it has technically moved out of my reach (dagger), but at the same time it is still inside my reach.