Mightshroom was an item that was only available at the Great Hunt, an event that started on March 20th and ended on April 2nd. Mightshroom was a replacement for the Item Elixir of Fortitude with the same stats.
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Elixir of Fortitude was a consumable item in League of Legends. Strategy It is often used...
(Note: This post is obsolete after the jungle overhaul in V4.20. I still think the ideas below...