Resilient Summons (Level 6 class feat)
[CONCENTRATE] [SPELLSHAPE] [SUMMONER]
Free Action
You can bolster your summoned creatures with your own life force. If the next action you use is to Cast a Spell that has the summon trait, the creature you conjure shares your hit points in the same manner as your eidolon. The summon still ends when the spell's duration expires. If the spell conjures more than one creature, choose only one to benefit. This feat does not apply to summon spells with the incarnate trait.
Workable?
Balanced?
Thoughts?
I do not really see the benefit. A rather large part of the appeal/utility of a summon spell is that they can be attacked in the place of a PC, and have a real HP pool.
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If you want this to be a desirable feat / metamagic, I'd suggest this instead:
[...] that has the summon trait, the creature you conjure gains or increases its resistance to all damage equal to your level. All damage the creature reduces via this effect is instead taken from your own HP. [...]
The caster wants the summons to survive, but also wants the summon to lose some HP (instead of themself). This change would allow the summons to be a lot more tanky, but still let the Summoner benefit from their HP pool.
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In my opinion, because this feat is limited to a niche that's notoriously "not great" and does literally nothing else for the Summoner, I'd buff it further.
Instead of loosing HP for all dmg resisted, I'd say "... for half the damage resisted" would still be perfectly balanced.
You could even go further, and say that the damage is reduced by the Summoner's level (or half the Summoner's level), then split evenly between the caster and summon. No need for adding resist all, which simplifies things.
"Lifelinked Summons" is also a more descriptive name. I would never expect something called "Resilient Summons" to substitute my HP like that.
Don't feel afraid to make a niche class feat actually potent.
I was thinking that a feat that kept a summon in the fight as long as the summoner was already pretty potent. That's more time to use its special abilities.
The lifelink also serves as a balancing factor that fundamentally changes how the summoner might want to use their summon. In hindsight, I didn't think of the summon's lower AC/saves though. It would suck to eat a bunch of crits aimed at the summoned creature.
I like the idea of adding something to mitigate that, such as resist all equal to the summoner's level, or perhaps even shared defensive stats.
I quite like the idea of making summon spells work more like eidolons, and wrote a brew a while ago that proposes summon spells to that effect. HP is not the only measure of a creature's durability, however, and because summons tend to have really poor AC, summoning a creature linked to your HP without any alterations to their AC is likely to get you killed very quickly through crit after crit. The Summoner works not only because they have extremely high HP for a caster (the highest, in fact), but also because their eidolon has the AC of an at-level martial class, and without those two things the class would likely not work well at all.
With this in mind, I would suggest a couple of things: the first is for the spellshape to provide temporary HP scaling with the spell's rank, so that you get a bit of a buffer, and the second is to set the summon's AC to some minimum level, such as your spell DC. Trip H. I think also proposes a much more workable alternative, where instead of eliminating the summon's HP and using your own, the spellshape gives the summon resistance to all damage and causes you to take the damage that gets resisted. I would suggest the latter rather than the eidolon conversion, because short of reworking the summon trait and every summon spell around it (like in the above brew), the full HP link is likely to be too harsh on the caster for it to be worth it most of the time.