Always see particle/mob texture

I'm trying to make a "death timer" type of mechanic that features a creepy thing that gets closer and closer to the player, indicating the time they have left. I want this to be either a client sided particle or a global entity that the targeted player can see trough blocks, basically seeing the inevitable as it approaches from wherever it is. The issue is that i can't find a way to make the player see this thing trough blocks.