Cavern of Lost Hope

{t}: Add {1} to your mana pool.
{7}: Exile target creature.
{w}{u}{b}{r}{g}, {t}: Exile all permanents, then each player may put any number of other cards they own from outside the game into their hand. Each player adds {x} mana to their mana pool, where X is the number of permanents that they own that were exiled with Cavern of Lost Hope. This mana does not empty from their mana pool as steps and phases end.