For those too lazy to click the link:
"Sie mag ihn am meisten" = "She likes him the most" (ihn being accusative)
"Sie mag er am meisten" = "[it is] she, he likes the most" (er being nominative)
another translation could be "He likes you the most."
How come it can't be the formal 'you'? Making the sentence: He likes you the most
Why is 'meisten' the most, when the meaning is said to be 'mostly' or 'for the most part'?
"er" is only capitalized if it is on the front of the sentence. The personal pronoun that is always capitalized is the formal Sie.
I'm not sure if this is the best place to report this, but in the listening section I got the error: 'In accusative case, use "meisten" for undefined nouns like ""' when I entered Sie mag er am meisen. So that appears to be a bug. Again, not a language issue, but I don't know where else to report this.
Ahhhh I see! Forget the word order, look at the pronouns! Sie can also mean "her" in Accusative, while "him" would be "ihn"! Considering the word order the best translation would be something like "She is the one whom he likes the most"!