Nothing stops a warlock from wielding a light pact weapon in one hand and a shadow blade in the other. With that combination, you could attack twice with Thirsting Blade and make a bonus action attack with the shadow blade. I'm still confused, new to light weapon fighting. How is there an attack with bonus action? Thirsting Blade gives 2 attacks with pact weapon only. Does the Shadow Blade always cost a bonus action? Thought it was just a bonus to cast, and then you use like normal weapon.
— Travis Dvoracek (@LedeshHevent) November 15, 2017
Because the shadow blade is a light weapon, you can use it with the rule on two-weapon fighting in the Player's Handbook (see p. 195). #DnD https://t.co/myYUEigtRF
— Jeremy Crawford (@JeremyECrawford) November 15, 2017
Cool as it sounds, doesn’t it only become a net gain of attacks on round 4? I wouldn't recommend casting shadow blade if your primary goal is to increase your number of attacks.
— Jeremy Crawford (@JeremyECrawford) November 15, 2017
So every time you make an attack with Shadowblade, is it considered as a bonus action? For example I can cast a cantrip then use Shadowblade?
Nothing in the spell description indicates that you don’t follow the usual rules for Action Economy with SB than as-normal (if you want to attack with it, you must use the Attack Action, or use it as a main-or-off-hand Bonus Action Attack when you use AA, treating it as a main or off-hand weapon). Unlike with Spiritual Weapon, which specifically cites how it is used as a BA regardless of what you use your Action for, SB has no such ability. It’s a BA when you cast it; whether or not it’s a BA when you *use* it depends on if it’s your off-hand weapon for the AA.
Sidenote: I think JC’s comment, vis-a-vis not using SB if your goal is to increase your number of attacks, is perhaps miscontextualized. While you wouldn’t have the off-hand attack with it on the round you cast it (because it costs a BA to cast, and again unlike SW it doesn’t also attack as part of the casting), it lasts one minute and is a very powerful weapon — especially when used for off-hand attacks — as it does psychic damage (of which the vast majority of opponents will be affected by) and has other circumstantial perks (such as when fighting in low light or darkness). It only “impedes” on having the extra BA attack (assuming using the AA as you Action) during the turn/round it is cast; after that, it’s usable as an weapon just like any other (except, of course, requiring concentration to maintain, so damage to the caster may disrupt it).