Is that verse or prose at the end?
The syllable count is strange, when I try to chant it like verse it doesn’t work.
2nd question, how do you translate the term asita in that verse? B.Bodhi goes with “unattached”, I stick with the literal dictionary definition “eaten their fill”, not sure exactly what is taken as the object of being eaten.
3rd question, how should “tusita” be understood in this context? B.Bodhi goes with “contented and unstirred”, presumably that’s the chief characteristic of tusita deva realm. I’m wondering if just leaving “tusita” untranslated might be better, perhaps indicating that the minimum one could expect of performing right exertion properly is tusita rebirth.
(those who) rightly-exert,
they’ve eaten [enough, of]
Birth-(and)-death;-fear (of it) transcended.
They (are) contented,
jetvā māraṃ sa-vāhiniṃ
(having) conquered mara’s **-army,
they (are) free-of-lust,
sabbaṃ namuci-balaṃ upātivattā
all (of) deaths-power’s (they’ve) overcome.
They (are) happy.
Those who strive rightly
overcome the realm of Māra;
they are unattached,
gone beyond fear of birth and death.
88They are contented and unstirred,
having conquered Māra and his mount;
those happy ones have overcome
all Namuci’s armies.641"" 
You’re right, it is unusual. I have asked Ven Anandajoti about this, he’s the expert on meter. I’ll let you know if I here back from him (he’s travelling in India right now, so internet is dodgy!)
Well, the dictionary gives four meanings, so it’s a matter of context. When it means “food” it is clearly associated with relevant words, as eg. at AN 5.29 (asitaṃ pītaṃ khāyitaṃ sāyitaṃ), AN 5.30 (Asitapītakhāyitasāyitassa), etc. But the current context is talking about freedome from samsara, so it must be “unattached”.
Incidentally, I would prefer “danger” instead of “fear” for bhaya here. Bhaya is used both in the external sense of something threatening, i.e. danger, and the internal sense, the emotional response to a threat, i.e. fear. Here, however, it doesn’t merely mean that you are emotionally undisturbed by the thought of death (which could apply to any psychologically well-balanced person): it means death is no longer a threat, i.e. you’ve made an end of rebirth.
Tusita means “contented”, aneñja is “unstirred”. In this context tusita cannot refer to the heaven realm, as it is talking about the end of rebirth and destroying Māra.
Ven Anandajoti found the time to email while packing to set out for Ajanta. He’s a very nice monk!
He analyzed the meter like this:
Te asitā jātimaraṇabhayassa pāragū;
Te tusitā jetvā māraṃ savāhiniṃ te anejā,
Sabbaṃ namucibalaṃ upātivattā te sukhitā ti
It is evidently trying to be a gaṇacchandas metre, but is very corrupt
Thanks for clearing up those points Bhante! And thanks to Ven. Ānandajoti for lending his expertise in meters.
I wasn’t sure if arahantship was definitely established until your explanation. In the next sutta, AN 4.14, the last line of the verse and sutta, “yehi bhikkhu idha aataapi, khaayam dukkhassa paapuneti” (destruction of suffering) seems really definite in declaring arahantship. In AN 4.13, I thought it might have been like those passages in AN 9 dealing with 9 samaapatti, where Mara is blindfolded in the 4 jhanas, and the meditator is invisible to mara in the first four formless attainments. If I recall correctly the 9th attainment also was only “invisible to mara”. In the four jhana case Mara’s supression is only temporary, so I thought in AN 4.13 might have been going for that angle.