These voice lines are triggered by killing jungle mobs
I think its very very very very likely a jungler.
"You will be missed old friend, warts and all. "
"Goodbye Gromp, or as you would say, ribbit. "
"Hop to that lilypad in the sky, old friend. "
"Next time, more petting and less stabbing. "
"A tragic end for such a noble friend."
"Why kill when you can simply ask?"
Could be like Kindred's mark lines but instead of him hunting down marks its triggered randomly sometimes when someone kills a jg mob as to go with the whole "be nice to wild life/ be friends with animals" vibe.
He could be a support (or laner I guess) who, like Bard, gets buffed from roaming the map. But unlike Bard his gimmick comes from going to JG camps and doing something other than killing them cause he clearly advocates "more petting and less stabbing" and generally being friends with the JG mobs.
Given how wacky Riot has been lately I wouldn't put anything pass them.