If you're at all interested in the plot of Path of Radiance and Radiant Dawn and don't want anything major about it spoiled, I would suggest not reading this one.
4. Sephiran/Lehran (Radiant Dawn 4-E-4)
The boss you can't even reference by either of his names without giving away a lot about the story! Though in fairness, I imagine most people got the sense there was probably something up with him from his first appearance in Path of Radiance, what with him possessing a skill that makes him literally invincible and all.
I'll be sticking to calling him Sephiran since that's what he's referred to as throughout the games by far the most often.
Anyway. Sephiran shows up looking somewhat underwhelming on first glance compared to the bonkers stats of the previous boss, Dheginsea. With only half as much HP, noticeably worse defensive stats, way less attack and his only seeming advantage being extra speed that is partially counter-acted by his tome weighing him down for some reason, leaving him at a mere 2 AS higher than the dragon king, he doesn't exactly look the part of a penultimate boss. Even the free +10 defense he gets from an item in his inventory that brings him up to 35 doesn't exactly impress after the ludicrous 50 defense Dheginsea had. But despite this, Sephiran manages to be much more interesting than the straightforward "your stats must be this high to fight me" approach his predecessor brought to the table.
First off, his seemingly minor 2 AS advantage is actually kind of important, as very few non-laguz classes have a speed cap that can double 32 AS. In fact, it's only Trueblade, Seraph Knight (none of whom are really good units due to availability issues), Whisper (neither of whom are even vaguely functional for combat at this stage), Ike and Volke, and Ike often requires some BEXP abuse to reach that kind of speed on his own. Even the monstrous Caineghis falls short at 34 speed, making for one of the very rare advantages Giffca has over him. Though the other laguz royals can double no problem and you have Nasir's White Pool to give +5 speed to anyone adjacent to him to help out, it nonetheless limits your options for units who can dish out significant damage.
And that's an important point because you can find yourself running low on units to attack with due to the main gimmick Sephiran brings to the table, which is the enemy spirits on the map. Not that they're overly powerful or anything, of course. Their ability to teleport around makes them a nuisance, but they're not too threatening to most units and only some of them move at first, plus the floor is full of wardwood tiles that give you a huge resistance buff, enough to handle their attacks quite comfortably. The actual problem is that the four spirits surrounding Sephiran himself will take otherwise lethal attacks aimed at him, forcing you to kill them off to be able to actually take him on directly. And they respawn every turn. And Sephiran himself heals 40 HP every turn, preventing you from just chipping him down over time.
So actually killing this guy is surprisingly complex, especially if you want to do it quickly (and you do, given that he has some nasty map attacks to throw out). You need to cover a lot of ground to get to him, then cut through all of his protectors (who come on defensive terrain, naturally) and only then can you actually finish him off, and while he's no Dheginsea his durability is still enough to keep that from being a mere formality. And if you try and fail, he can teleport across the map, bringing his guardian spirits with him, forcing you to do it all over again.
He also of course has Corona to potentially nuke anyone who lacks Nihil, but that's pretty much to be expected by this point. Does further limit your options and force you to not commit the people you gave Nihil to attacking spirits without good reason for fear they won't be able to help with Sephiran.
This chapter is generally very short with nothing to do but charge up and take on the boss, but it manages to be pretty interesting due to how tricky the process of setting up the boss kill can be. Sephiran is not exactly my favourite character, but his distinct gimmick in gameplay certainly makes for a cool battle.
Up next: No more spoiler text! A very strange boss with a very strange gimmick (both in gameplay and story) that can be solved with a clever exploitation of something that you could easily argue doesn't even qualify as a game mechanic.