Even As An Old Man, Wayne's Still The Master Of Ominous

'When all hope is lost. . . Spread the ash around you in a circle, open the book, and recite the marked passage. Use it only in Earth's final hour.' - Bruce Wayne, Batman Beyond Unlimited #8, "Konstriction"

So, what did Bruce give Terry for a last ditch weapon against the Ouroboros? It's something mystical, what with secret phrases and ash circles. It's powerful enough to actually be of use against something that shrugged off everything the Justice League, Apokolips, and New Genesis threw at it. And it's carries sufficient risk Wayne won't tell Terry what it does.

That last one could be for two reasons. It could be dangerous enough to the Earth he doesn't want Terry thinking it's the easy path to victory and using it when it isn't necessary. Or, it could be dangerous enough to Terry that Wayne doesn't want the kid hesitating to use it when it is necessary. Which still doesn't solve the question of what it is.

I thought Etrigan at first. The specific phrasing, the unwillingness to let Terry know, made me consider the possibility Blood and Etrigan had been separated, and this would bond Terry with the demon. Which should certainly qualify as a last resort. But I can't see Etrigan being that powerful, to succeed where everyone else failed. It would have to be something even higher up the ladder. Or lower, as the case may be.

Of things I can think of, there's Eclipso or the Spectre (I considered the Phantom Stranger, but this seems like a situation calling for direct intervention, which is rarely the Stranger's bag). Either might be powerful enough to turn the tide, and bringing either one into the mix could be seriously dangerous. Especially if Terry has to act as host (though there's a chance the ash is a protective measure for him). Calling up Eclipso would certainly carry a sizable risk, and depending on his disposition, the Spectre would be pretty dicey as well. Sometimes he can be friendly, other times he acts fairly contemptuous of mortals.

I don't know, I can't think of any other characters that Bruce would consider summoning that could make a difference. Unless it's some sort of binding or sleep spell, which doesn't seem like the sort of thing to entrust to a magical novice.