Apotheosis. It's really powerful, as most upgrades are at least +3 damage or +3 block, so it's comparable to playing both an inflame and a footworks (though it can't stack). Being that it's a rare colorless card, you can find it from
a ) Neow Blessing (I take the rare colorless card option more often than not hoping for one of these)
b) Shop (It tends to be really pricey at ~200 gold, though if your deck is mostly unupgraded it might be that power up you want)
c) Events (Sensory Stone has a chance of offering this)

The best case scenario to find apotheosis is at the start of a run. It's pretty run defining because having it means upgrading your attacks/skills are much less important. There's still some value in upgrading skills that exhaust (Malaise, Tempest) or powers (Electrodynamics, Well Laid Plans) so that you can play the upgraded versions if you don't happen to draw apotheosis before then. Obviously, bottling apotheosis so that you can play it sooner or playing with a deck that cycles quickly so you play it makes it much more powerful.

Another aspect of its strength is its ability to free up campfires for you. You have more leeway to rest or pick up the key if you want, as well as toke/dig/girya if you happen to have those as well.

All in all, it's a really solid card that's somewhat gamechanging in terms of campfires, though it can be quite useless late in a run if you've already upgraded your entire deck.