It's not really funny at all, by the "companion who is killed every other episode" it's referring to Rory (the guy on the phone at the bottom) as the series he was in had him dying every other week and then somehow coming back to life, and the "killed in every episode" is the woman above Rory, Clara. She doesn't miraculously come back to life, there's another version of her in every time period and it just so happens that they all die in their episodes.
But.. that's just what the image means.. it's not really funny