@13orgI mean, Senna's far from unkillable and she was hurting after that attack? One more attack and she would have been KO'ed pretty badly.
Senna is a glass cannon too, and I built her specifically to have some of the weakest natural defense in game. She's just built her skills around being able to be less squishy to make up for it. The armor, for example, which didn't even stop Selena's normal attack (and Selena isn't even a melee character), and amulet which reduced the effectiveness of magic by a small bit - enough to ward against lower level magic but was basically useless against that artillery spell.
Keep in mind senna literally can't be crippled thanks to her 'Tireless Rage' skill, which means she can fight and move at full effectiveness despite any damage to her body, as well as any physical ailments. Its really just a skill specifically built to mask how much damage she's taken unless somebody has some sort of analyzing ability. A scare and intimidation tactic since someone seeing someone taking a nuke to the face and seemingly being able to shrug it off would cause a pretty huge effect on morale.
As I said, that attack did some pretty heavy damage to Senna. She's just not showing it because she literally can just ignore any pain and fight and move at full capacity - and Selena's curses
are working. They're just not working as well as she intends because of Senna's resistance to both mental and physical interference. If they weren't working, the Senna wouldn't have been injured by Selena in the first place, nor would she be running to the fort for healing fodder. She'd probably actually have gotten bored and ended up leaving.
If Yasha would have followed it up with another attack (and hit, mind you, since Senna's entire fighting style is built around dodging damage instead of tanking except in cases where she can't dodge) then Senna would have pretty much been dead. Senna can basically take about three hits from any of the PC's and NPC's before dying if she's not able to heal between hits. That's something I've determined from the start of the game to keep things a bit fair.
Yes, senna is a powerful and troublesome opponent, especially if there's weaker lower-leveled people around that she can basically just use as healing fodder, but she's far from unbeatable. Keep in mind that all of our characters are pretty much around the same level, more or less, meaning I don't think there's going to be any one-shotting going on no matter what. That'd just be rather...much. I suppose that's more of something for the GM to decide, though.
I don't think there is anything Yasha can do... Her shots, even coming from a rifle (with a target finding spell) can't hit Sena, it doesn't matter if she conceals her presence before taking the shot.
What exactly do you mean with a 'target finding spell'? You mean heat seeking bullets? I assumed that was a simple spell to track a target and fire an optimal trajectory (correct me if I'm wrong on that) But even so, Senna's both flexible enough and agile enough to avoid it or simply turn Bloodlust into a giant slab of a sword and block it. She has to be, or Senna wouldn't be a threat at all and have already been defeated.
Not trying to be hostile or defensive here, but I feel like I need to explain a few aspects about the character and the skills.