Release champion balance has always been an imperfect science. Before a champion is revealed, we playtest new champions and make iterations constantly, trying to make sure we get as close as possible to “perfect” balance as we can. Sometimes we’re off in either direction—too weak (Ornn most recently) or too strong (Camille). Sometimes we get it right (Kled).

One of the more important factors that affects a champion’s power on release is their mastery curve. Simply put, a champion’s mastery curve is their expected growth in power relative to how many games a player puts in on them. Since champions must be balanced assuming the person playing them is experienced, a champion with a high mastery curve (such as Yasuo) will have a very low win rate for first time players that rises significantly over time; a champion with a low mastery curve (such as Braum) will start higher but have much less growth relative to their true balance state.

The aspects of champions that create high mastery curves are usually the same reasons it can be difficult to gauge how powerful a champion will be on release. New mechanics that don’t have strong analogues in the game already (such as Ornn’s passives), subtle mechanics that require a lot of optimization that may not be obvious (such as Ornn’s brittle effect or his items), and difficult to execute mechanics (such as Ornn’s second cast of his ult) all combine to add to the difficulty of estimating power levels. Quite frankly, these factors can all make it easy for us to make mistakes—especially considering the limited amount of data we have to work with relative to the millions of games we have on Live.

Compounding all of this is the human element. For example, our best Ornn player internally routinely smashed games right up to release, performing better on Ornn than any other champion he played. We took this as a sign of Ornn’s strength, but it is possible that he was an Ornn one trick in the making. Conversely, our Aurelion Sol players never discovered some of the optimizations that are now routine for seasoned ASol vets, which contributed to a champion who was overbearingly powerful a month or so after release.

At the end of the day, no one on champion team wants their champion to release unbalanced. Weak can mean poor reception, and strong can mean nerfs that will cause player pain going forward. We try to get as close as we can, and we’re lucky enough that we are able to respond fairly quickly if we’re off.