So I have been working with the Obelisk on Thingiverse:
https://www.thingiverse.com/thing:3646449
I see them with a d20 power when you are next to them.
If a unique hero starts their turn next to a Obelisk and does not leave engagement with the Obelisk during their movement, they roll a D20 and apply the following affect before they attack:
1-5 nothing happens
6-8 -1 defense until you leave the obelisk (bummer)
9-11 counterstrike against normal ranged attacks (it is magical)
12-14 +1 attack until you leave the obelisk
15-17 +1 defense until you leave the obelisk
18-20 teleport to another Obelisk (not sure how to choose if there is more than one more on the board).
this is what I was thinking. You could do less powers that are more powerful, with it harder to get. I like board touchstones that can be chaotic. Kind of a hero support (unless you roll under 8, obelisks can be tricky). They could come in a 2 or 4 pack for the board, depending on board size.