Rakdos Charm Almost all the cards in the guild charm cycle are pretty solid cards
The best cards to splash are single pip removal and busted rares
With firebending, this can become a powerful creature on its own, and it technically repays for 66% of its mana cost the turn it's played, as it costs 6 mana but generates 4 with firebending
Stock Up is likely better for a deck that wants to play at Sorcery speed, but a good chance this is better for a deck that wants to play at instant speed
All that being said, it's got a high ceiling and a low floor, and is probably over costed
Jace has also inspired some of the game's most powerful and intriguing Planeswalker cards, most notoriously the Jace, the Mind Sculptor mythic rare card from the 2010 Worldwake set