1. A slight feature idea is that if you stay in one spot while holding down you can gradually speed up digestion, useful for those that want to consume as much of the ecosystem nearby as possible in a cycle.

2. Now, a idea. though I note I don't know how difficult to implement this would be, maybe spearmaster could still be able to eat creatures, just storing and shoving them into their tail instead of stomach.

Per slugcat config and “capacity” system.
First, the per slugcat system idea.
Basically, the current config would be the “global” config, and each slugcat could be configured to use their own config, (also I suggest with this to have 2 presets of “global” and “per-slugcat” for defaults for easy setup)
Though the current digest speed doesn’t fully detail, if for example it took 15 ticks to deal 1 damage, then artificer would by default do 1 damage every 8 ticks instead, I think you get the idea.
Also I’m not gonna detail this a ton because message limit, but slugcats could also have per-slugcat difficulty to escape.
This brings up now the second idea, the capacity system, which is made to work with per-slugcat config.
How does capacity work? Capacity reduces/increases struggle effectiveness of prey. So if you eat something tiny, it’s not gonna escape, but if you eat a lot of tiny things, they are more likely too. (Struggle strength would be based off total mass of all live prey inside, so you don’t have constant struggle spam, and struggles can simply be all at once periodically)
Capacity then allows each slugcat to further feel unique with how they consume the ecosystem, eg artificer having a very low capacity but very high digest speed versus (if my other suggestion is implemented) spearmaster who would have a high capacity and mediocre digest speed, and medium difficulty to escape. Whereas Saint would have a very high capacity and be near impossible to escape, but very slow digest speed, etc.

Revive/heal prey/predator
Similar to hungry lizards config, where you could feed yourself to a ally slugcat to heal and revive them (whether needed to be in den or not configurable same) or they could eat you to revive/heal you, (whether revive is possible or only heal and whether den needed again, configurable.)
Also config for eating tamed lizards to heal/revive them, (if possible this probably should increase lizard rep.)

add-on for hungry lizards idea: expanded noms
While lizards can eat the slugcats and the slugcats can eat a lot of the ecosystem, the ecosystem can’t really eat each other.
So what if they could? Basically hungry lizards but for creatures to be able to vore each other. Also options for expanding some hungry lizards features to other creatures (including the effects of the mod itself) even those it wouldn’t make much sense for fully.
Some of those creatures being: leviathans (basically already done for them, just need digest functionality and struggling to be futile and done), rot (the core could expand similar to rotund world, and of course that’s their “stomach done”), vultures (basically they could swallow prey now), Miros birds (similar to vultures), centipedes and their variants (one end could be a “mouth” and they swallow prey down into their center from there to be turned into more “fuel” after digesting in their center), stowaways (sometimes instead of biting prey they could just eat them whole), stowaways (again mostly done like leviathans), big spiders (swallowing prey whole after paralyzing via bite/darts), giant jellyfish (yet again almost done already just like leviathans), inspectors (similar to rot, their behavior could be modified so they sometimes grab and swallow player instead of throwing stuff at them), and finally scavengers (similar to slugcat, just buffed most vore related ways at cost of reduced digest speed)
I think that’s all the creature it would be feasible to implement such for, most others aren’t predators or are unique in ways that make having a “stomach” not possible.

Also a final change from this addon (able to be disabled in settings) being digested prevents reviving as there isn’t anything to revive. So yes you could see it up to revive in an unfriendly predator and do so, but if you digest before you escape, you won’t revive again as you have been completely melted away already.

Further add on for expanded noms idea: Expanded noms outskirts
This addon could take the mods effects yet further adding its effects to creatures it doesn’t make sense for in the other mods including normally prey creatures that could now have a chance to decide to just attempt to eat the ecosystem nearby them.
Some creatures this mod would apply to: pole plants and Monster kelp (who would simply gain a “stomach” near their base), squidcadas, Coalescipedes (who could take a long time to swallow player but be very hard to escape due to how tight a squeeze it would be, with the largest spider in the chain doing so, meaning the spider doing so needs to basically be the head of the Coalescipede as those are the largest ones), Raindeer (who would occasionally try to swallow creatures instead of let them onto their horns), Nootflies (who could invert their nose from stabbing to suction occasionally), lantern mice (similar to a slugcat, again struggles to swallow creatures more but hard to escape due to how tight a squeeze it is), jetfish (similar to others, though not as hard to escape, they use force to slide prey down but they can just slide right back out with enough effort), yeek (similar to jet fish, very good at swallowing, but harder to escape, though slow digestion to balance out)
All other creatures are too small and wouldn’t really work due to rainworlds engine because it likely would just spam fling the creature around if a stomach was attempted to be added (eg batflies).

No hard vore option: slugcats prey from base game is swallowed whole instead of in pieces, eg baby centipedes, baby noot flies.
(Maybe if don’t eat the spiders mod is also installed and enabled those too are swallowed whole)

Greedy stomach option: Depending on item rarity and cycle length items will digest over course of cycle (does not apply to key items unless a seperate toggle to allow those to digest also is enabled whereupon the key item respawns where it was digested next cycle)
Not affected by digest speed, just cycle length and rarity, so that it’s roughly same rate for pearls in that campaign.
(Eg normal pearls digest in 35% of the cycle, overseer eyes take 80% of the cycle to digest)

For sake of organization and in case comment is buried, feature request by Soniciscrazy05_RBLX

"An Idea I have for this mod. Add a toggle in the remix menu to not digest friendlys/tamed creatures? (Example: Lizards.)"

Would be neat to be able to pick what thing you want to regurgitate. Too often I find myself wanting to use my stored item but I can't because I'll free something that'll kill me.

Being able to swallow more than 1 object would be cool too

Delay between digestion and absorption of creatures; if rotund world is enabled, a creature turns into pips only when absorbed, adding more size than the pips its worth until absorbed.
If rotund world is disabled, basically player will be larger for longer, and need to absorb digested prey.

More “ambient” movements.
Eg slight movement of slugcat stomach as they breath, similar to hungry lizards.
“Soft” struggles, that don’t actually affect fatigue, that are essentially much weaker struggles to visually jostle the slugcats stomach around more, with effect increasing the more prey inside.

Instead of making suppression of struggles be simply by crouching, make it additionally vary based on how much the stomach is being squished at the moment of the struggle, making being in the open possibly be more dangerous as prey could escape easier BUT also more potential reward with squishing into/through pipes, due to it squeezing the stomach tight enough nothing can get through.

Ability (configurable in settings) to grab onto room travel pipes and while doing so automatically hold your mouth over them, causing creatures to unaware, travel from pipe directly into slug stomach.

Originally posted by TheGreatGreenStar:

Greedy stomach option: Depending on item rarity and cycle length items will digest over course of cycle (does not apply to key items unless a seperate toggle to allow those to digest also is enabled whereupon the key item respawns where it was digested next cycle)
Not affected by digest speed, just cycle length and rarity, so that it’s roughly same rate for pearls in that campaign.
(Eg normal pearls digest in 35% of the cycle, overseer eyes take 80% of the cycle to digest)

please.....

Slugpups aren't saved by the slugcat immunity. While we're at it, a setting to have slugpups and stuff not struggle would be nice. Another nice thing would be if the more non-squirming pips you have, the less a struggle will affect you. Prey's gotta work through all that muck.