Can Niall rummage around in your character’s mind? He can try! It might be difficult seeing as he's spent a good portion of his life with a telepath occupying his head, so I imagine if another telepath entered his head and he didn't recognize their "touch", it might turn ugly fast.
If yes, what stuff might he find there? Would he have difficulties? As above, Niall would have difficulties. Conner would block him out immediately. Or try. What he might find if he pushed hard enough would be thoughts and memories, emotions concerning Artemis's death, his break up with M'gann (despite how they're back together in Exsilium), Kaldur's betrayal to the team and all that jazz.
Can Niall manipulate your character’s emotions? Sure!
Can Niall inflict hallucinations on your character? Yes. Definitely.
no subject
If yes, what stuff might he find there? Would he have difficulties? As above, Niall would have difficulties. Conner would block him out immediately. Or try. What he might find if he pushed hard enough would be thoughts and memories, emotions concerning Artemis's death, his break up with M'gann (despite how they're back together in Exsilium), Kaldur's betrayal to the team and all that jazz.
Can Niall manipulate your character’s emotions? Sure!
Can Niall inflict hallucinations on your character? Yes. Definitely.
Any other stuff you feel I should know? c: