The Portal Around
The Portal Around is a power Legendary item that allows the heroes to open a portal around a problem. It is a small hand mirror decorated with many unidentifiable jewels.
To use the Portal, the heroes must clearly state what they want solved - perhaps they need to travel from one place to another, sneak past a group of enemies, get a medicine to heal someone, or learn a key piece of information - then pull open the mirror and step through the portal.
Once they step in, time in the real world freezes, and they find themselves in a strange world that makes no sense. They may find endless fields, abandoned skyscrapers, a flooded desert, or any other kind of strange environments. They also will, almost certainly, find very dangerous inhabitants.
If they overcome the environment and it's inhabitants, their goal will be accomplished. They will find another portal somewhere, which will lead them to where they need to be. If they need a specific item, they will find it - then have to return where they came from.
The Portal will make heroes face a Very Deadly encounter (150% level) but the foes should have cryptic, confusing mechanics that shock the heroes, not just be balls or stats. The Portal can only be used once per safe rest.