Breakdown of Тот, у кого есть волшебный меч, сможет победить всех.
кто
who / whoever
у
at, by
есть
is, there is, to have
тот
that
Questions & Answers about Тот, у кого есть волшебный меч, сможет победить всех.
Why is it у кого instead of just кто after Тот?
The main subject is Тот (the one). The phrase у кого есть волшебный меч is a relative clause describing that person. Because Russian expresses 'to have' as 'by someone is', the pronoun кто (who) changes to the genitive кого to follow the preposition у. The two correlative pronouns (Тот and кого) do not have to be in the same case.
How do the commas work in this sentence?
The relative clause у кого есть волшебный меч (who has a magic sword) is tucked inside the main sentence Тот сможет победить всех (The one will be able to defeat everyone). In Russian grammar, you must always place commas around the entire inserted relative clause to separate it from the main sentence.
Why use сможет instead of может?
сможет is the perfective future form of the verb мочь (to be able to). The sentence describes a future result: having the sword means he will be able to defeat everyone. If you used the imperfective может, it would mean he currently is able to (present tense).
Why does the sentence end with всех rather than все?