Shireneko
A communication card can really be op in these occasions of Dungeon exploration, you can make it only work outside of the dungeon or inste it justifying magic interference because of the sealing lower of the tower. It can be used to coordinate between party's, scouts notifying of danger ahead and so much more
But I really think, that even with great variability the power need to be limited some way. like he can't resurrect someone if it has passed some time, permanent buffs are a big no because of mana consumption but you can make a nerfed versions when he level up like a mana collection card with a simple small buff or slowly putting mana in a card, or helping regenerate mana or stamina. So many ideas and possibilities