Should a true final boss be easier if reaching it is already the challenge?
I'm making a roguelite autobattler, and we're currently working on a true final boss. Think something like the Heart in Slay the Spire or Heart of the Storm in Wildfrost.
To reach it, the player will need to make sacrifices during the run: units, rewards, resources, etc. So I'm wondering if the actual boss fight should be a bit easier than our regular final boss, since a lot of the difficulty already comes from reaching it in a weakened state.
The main thing I'm worried about is frustration. In an autobattler, most of the player's agency happens before the fight: building the team, finding synergies, choosing items and positioning units. Once the fight starts, there isn't that much you can do.
That makes specific boss mechanics tricky. A boss spawning lots of minions naturally favors AOE. A long fight favors sustain. A mechanic targeting one important unit can completely screw some builds while barely affecting others.
Of course, the player can lose once, learn the boss, and prepare better on the next run. But if they already struggled just to reach that fight, I'm not sure getting hard-countered by something they couldn't know beforehand feels great.
One idea is to make the fight feel harder than it statistically is. For example, the boss could be stronger while most of your team is alive, then weaken as your units die. Strong teams would still lose some units and get that "oh shit, I might lose" moment, while weaker teams could potentially scrape through at the end.
Another option would be making the true final boss always available and very hard, but completing the sacrifices gives you a passive bonus that makes the fight much easier.
Do you think a true final boss needs to be the hardest fight in the game, or can the main challenge be earning your way to it?