I blocked T-Pein. I was waiting for him to reveal his results, to see if he would claim he had them.
Reason I blocked T-Pein, was that I was originally going to block Night Raid. However, after the hosts confirmed to me that eliminated factions will not be confirmed eliminated, blocking Night Raid, who at that point was my strongest read for a fourth Mafia member, wouldn't have helped figure that out at all. If there was no kill, it could be because I blocked Night Raid, or it could be that the kill failed through other means, or it could be that there is no other Mafia member.
Therefore, I had to block someone who was extremely unlikely to be Mafia, and had in-thread credibility to back that up. In my view that list is three names long, because of their push on Rej: myself, Emi and T-Pein. I'm obviously not going to block myself, and Emi at least had information pertaining to their role on the table, which leaves T-Pein. There does exist the possibility that T-Pein was Culted, failed to recruit Rej due to him being scum, or otherwise investigated Rej, and then exposed him to gain credibility with the Town. It's not all that likely a scenario, but it's a possibility in play. That way, if a kill does go off, I can be more certain that there is a fourth Mafia member (and it did, and hasn't been claimed by the Town).
In short, I used my block on T-Pein, to help test my theory by ensuring my block wasn't going to hit the Mafia.