Looking at Rhonin again, I think he's even worse and unplayable.
When you can actually play this? We have amazing cards like Ysera, but how often you can actually play that? you need to be in some level of control and safety to play Ysera or similar slower but good cards.
Now mage has Ice Block, maybe you can create a situation like that that you play this card or behind a belcher but what happens when you don't is that more often than not is going to get ignored by the opponent, not even silenced. If you don't have board advantage opponents just go face. You played a over priced war golem there, the thing is against a zoo deck for example you might not be able to kill your Rhonin by running it into some minion even, he can very often just get stuck there and not giving you your AMs you were expecting for some combo next turn. Sure you can maybe go face, but then you better have a plan B ready for this deck to finish. He's no finisher or even reliable enough to feed Antonidas for a finisher as mentioned earlier.
The most similar card I can think of is actually Tirion. It's a 8 drop like this but it's not a BGH target (actually which of the 8 drop legendary cards are a BGH target? Gruul and?) and on it's death it gives you something cool. The major difference is that opponent can't ignore Tirion cause he has taunt. They have to do something with it, silence or else. That makes it actually way way better than Rhonin. He should have had taunt too for its deathrattle to be useable often. Rhonin might be too slow to give you what you want, way too slow and might not do anything at all to win you any board control for 8 mana. Ysera is way faster than this actually, even one turn of it can give you a game changing card unlike this.
The other similar card is Dr. Boom, that obviously is way way better, no need to even explain there.
So while the deathrattle is quite strong, I don't think you can even get it 50 percent of times you get the opportunity to play it and the times that playing a card like this makes any sense seem rare. The deck must be really slow like grind or freeze mage, this has no place in a tempo mage deck and even in those decks I really don't think this will be favored by many. There are so many necessary big drops there like Alex, even Rag or maybe Malygos are better to me, that is a better fit than this card imo. You're not going to need this.
