create any world (superflat prefered)

put down obsidian in a line skipping a block every time, for a line of 30 long or so.

put crystals down on each of them, remove the obsidian

now hit any crystal at either end.

1: The line won't propagate all the way through

2: only the activated crystal explodes, not any adjacent, they solely get killed.

3: if you remove obsidian on one crystal and explode it next to the other, the other will turn into some kind of null entity that doesn't display in the entity count, but blocks any ability to destroy blocks in the hitbox of the previously existing crystal (see video)