User blog comment:LivesByProxy/Summoner Spells Redux/@comment-26378838-20151226195735/@comment-26378838-20151228172629

"I would like to see such an effect, but I'm not sure how to word it because we have no precident. Even if we did, I fear it would still result in a very wordy tool-tip. @-@"

While we have no precedent of spell-bouncing, we already two mechanics that deny abilities, which is the first component of such concept: walls like Wind Wall and Unbreakable and the spell shields from Fiora, Nocturne and Sivir. The former intercepts projectiles and deny their damage, the latter simply blocks abilities entirely. If we build spell-bouncing from those components, we'd have two versions:

A) Creates a barrier seconds that intercepts the first incoming enemy  projectile ability that hits within the next X seconds,  negating its  damage  and redirecting it back to its caster. Y seconds cooldown.

B) Cr eates a barrier that blocks the next enemy  ability  that hits within the next X  seconds and redirects it back to its caster. Skillshots will be redirected with a vector opposite to the original. Y seconds cooldown.

Version A would be more limited (non-projectile abilities like Lux's Final Spark wouldn't be bounced and non-damaging projectiles like Elise's Coccon wouldn't bounce their effect), but is more simple, both in wording and in coding.

Version B would have more uses, but considering skillshots work on vectors, you'd have to reverse the vectors to keep the thematic and a lot of bugs could creep out of the woodwork (specially with Azir, Emperor of the Bugs). Also you'd need to include the opposite vector bit for clarity sake, which adds to the verbosity.

About your previous creatable terrain spell idea, I think it could work like Trundle's pillar, just something to catch someone or laugh at Sion's ult being interrupted by an earthen middle finger.