Beings of Tash Kalar
Imagine three small totems or other ritual items placed carefully around the summon space.
The Ritual Master invokes natural magic of the summon space – energizing if it is green, destructive if it is red. On other spaces, this magic does not work.
The pattern is relatively tricky, as it has to be placed around a specific space to have an effect. You usually need to prepare it one round ahead. But it is worth it, especially if you prepare the pattern around a green space: if you summon the Ritual Master by your first action on your next turn, you get a heroic piece on board and still have three actions left. However, an experienced opponent can recognize the pattern and he probably will try to destroy it.
Ritual Master was created right after the original deck was split into schools, as it was at that time when I decided some Highland beings will be using space colors. Originally, it destroyed only one non-legendary piece when summoned on a red space, but other than that, his pattern and effect remained unchanged during development.