In regards to an artificer that selects the Returning Weapon infusion:
The infusion states that a thrown weapon immediately returns to its owner upon impact, but does not specify that it must return to the hand from which it was thrown. If the infusion is used on a handaxe or light hammer, which are both light and throwable weapons, can the weapon be returned to an off-hand allowing for a two-weapon strike with the same enchanted weapon? Additionally, if the artificer is a battle smith and takes his second attack, is it plausible the same infused light, throwable weapon could be used for four strikes in the same turn by trading back and forth the hand to which the weapon returns?
RAW, you have to be holding both weapons you intend to use for two weapon fighting at the same time. But I have a rogue in my game whom I allow to throw their returning dagger twice with two weapon fighting.
In any event, I don’t see how you could get four attacks on the same turn. If your DM allows two weapon fighting, which again is against the rules, you could get three: two with your action from Extra Attack and one with your bonus action.
[EDIT] Another thing to just stress how against the rules it is, two weapon fighting also explicitly requires a different light melee weapon.
In regards to an artificer that selects the Returning Weapon infusion:
The infusion states that a thrown weapon immediately returns to its owner upon impact, but does not specify that it must return to the hand from which it was thrown. If the infusion is used on a handaxe or light hammer, which are both light and throwable weapons, can the weapon be returned to an off-hand allowing for a two-weapon strike with the same enchanted weapon? Additionally, if the artificer is a battle smith and takes his second attack, is it plausible the same infused light, throwable weapon could be used for four strikes in the same turn by trading back and forth the hand to which the weapon returns?
RAW, you have to be holding both weapons you intend to use for two weapon fighting at the same time. But I have a rogue in my game whom I allow to throw their returning dagger twice with two weapon fighting.
In any event, I don’t see how you could get four attacks on the same turn. If your DM allows two weapon fighting, which again is against the rules, you could get three: two with your action from Extra Attack and one with your bonus action.
[EDIT] Another thing to just stress how against the rules it is, two weapon fighting also explicitly requires a different light melee weapon.