While there isnt going to be a perfect answer for every deck or metagame, Ive found that playing 4-6 is usually a good starting point
Dockside Extortionist | Illustration by Forrest Imel A Magic sets value is determined by the secondary market of Magic players and collectors , investment/finance folks, and the game stores, online and brick & mortar, that price according to the actual demand from people and the expected future demand
Not to mention theres no restriction for his mana
Offering a buff across your creatures, Vodalion Hexcatcher comes in at instant speed and can challenge your opponents noncreature spells
So long as you have two extra mana, you can pay four to return it to play with the Deathmantle attached to it while also creating four 1/1 Myr artifact creature tokens
If not, however, then the flexibility of Fiery ConfluenceFiery Confluence will come in handy, in all likelihood being one of the only artifact removal options in the deck, not to mention an additional utility creature board wipe if needed