Event/game mode concept

Summoners rift. No dragons or baron. At, say, 6:00, rift heralds spawn in both pits. But instead of letting you summon a herald, defeating one swaps a pair of stats that items grant. No changes to passives or champion abilities. Heralds respawn every 2 minutes.

Suppose ap granted by items becomes ad and vice versa. Deathcap suddenly grants massive ad, but still gives percentage ap. Suppose health and mana get swapped. Archangels gives tremendous health, but no mana, although the passive does refund per spell. Crit chance to armor to attack speed to magic resistance in some daisy chain. Maybe a visual effect on the pits to make clear which stats are currently being affected and how. Like a compass or something.