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I'm checking up on something our dm threw at us because it frankly seemed a little nuts. In the midst of a big fight a enemy cleric used boots of Dimension Step to appear out in the open on the battlefield during the day in line of sight of our party, like 60' away. She was invisible and hiding in plain sight. A few of our group had True Seeing running but spotting her required extremely hard Perception checks. This continued as she cast Destruction a couple times. She was basically hiding in plain sight while attacking us. The spells were not silenced or stilled. The dm explained that this is a special ability for clerics of Tiamat. I have never encountered anything like this in the rules. Does this make sense to anyone? or is this some homebrewed cheese?