If the game already has a strong Eastern theme, which is what it looks like from the title screen, I'd just leave it as "Maten Douji" or "Maten Doji" or some such. You could use the little furigana scroll on the lower right to spell out "Maten Douji" in English, or if you want to go the extra mile, you could whip up a proper "Maten Douji" logo to replace the kanji, and maybe use the scroll for a suitable subtitle. Like, say, "Conquest of the Crystal Palace"? :3
No offense, but I think it's a mistake to transliterate the title. Transliteration only carries over the form of the title, but it leaves behind the meaning. The title is a pun, which we all know can rarely be translated (and still have the same effect), but still, I think it's possible to render it somewhat faithfully.
The title 魔天童子 is a play on the main character's name, 天童 ("heavenly/angelic child"). The title literally means "demon-angel child". AFAIK 魔天 is short for 悪魔と天使, which means "demon(s) and angel(s)"; 童子 means "child". He has to climb a mountain called 魔天山.
I'd suggest something like "Tendou: the Angelic Child vs. the Demonic Mountain". At the very least, I'd use the main character's name as the main title of the game.