Rust monsters are not that dangerous, really. Annoying, potentially very expensive to deal with, and often leaving you terminally unprepared for whatever comes next, sure. But not dangerous by themselves. Some eat metal. Others magic. Not this one, though. This one eats your destiny. You’ll survive the encounter, covered in the rusty flakes of your once-great future.
Fatum phages show up at the most unfortunate time. The closer a hero is to fulfilling their destiny, the brighter they shine in the multi-faceted eyes of these beasts. And if said hero’s One Unique Thing has something to do with prophecy or fate, fatum phages would stop at nothing to get them.
Level 8 spoiler [ABERRATION]
Caustic bite +13 vs. MD (one creature with no unspent story-guide icon relationship rolls)—38 damage, and 10 ongoing acid damage
Natural 16+: the target makes a save or permanently loses one of its icon relationships.
Rusting antenna +13 vs. MD (one creature with an unspent story-guide icon relationship roll of 5 or 6)—22 damage, and the target makes a hard save or decrements one of its story-guide icon relationship dice from 6 to 5, or loses a 5 entirely.
Tasty Tasty Fate: A fatum phage can add the escalation die to its attacks whenever it targets a creature that added the escalation die to its attacks last turn.
Rust’s targets: Icon relationships of creatures with 180 hp or more are not affected by the fatum phage’s ability to weaken or destroy them (they still take damage).
Rusted Icons: Pull up the Couatl entry of the Bestiary. Each time a fatum phage affects a relationship roll result or the relationship itself with its rusting antenna or caustic bite attack, it gains a corresponding icon-centric ability as if it was an 8th-level couatl. The fatum phage can only have one such ability at a time, so a new ability overwrites the old one; but limits on ability use such as 1/battle are reset when a new ability is gained.
PD 18 HP 144
Recovering Icon Relationships
The Archmage probably knows a useful ritual. So may the Elf Queen. The Diabolist likely has a deal she can offer. The Prince of Shadows stole everything there was to steal, maybe he knows how to unsteal some things, too. Point is, many icons can help. But why would they waste their time on someone so clearly insignificant as you?