"You tell it to him."
Translation:Du sagst es ihm.
I would interpret the English sentence as having a bit of attitude, kind of like encouraging someone to tell him something rather forcefully ("Yeah, he's totally wrong! You tell it to him, how it really is!"). Does the German sentence have this kind of feeling too, or is it rather neutral?
No, the German is neutral.
"You tell it to him!" in that sense would be Sag's ihm! or perhaps even Gib's ihm! (literally, "give it to him).
"You tell it to him (because I don't want to do so)!" would be Sag du es ihm! -- as with English, the pronoun of an imperative sentence can be mentioned explicitly to emphasise it, but it goes after the verb in German.
"sagen" is a bit more versatile than "to say". "erzählen" should work here too.
erzählen is a bit more like "narrate" -- you'd use it for telling a story, for example.
You can also use it for telling someone some information, but you can also use sagen for that. The feel is slightly different as erzählen still has this "story" feel to it a little, while sagen is more neutral.