You have to think about your first move carefully your opponent got one of these. As for the names, you can imagine an army of soldiers moving them XD. Frostress roaming the chess board no problem.

They can only move like rook or bishop while not attacking and must leap over exactly 1 unit in order to attack.

If given shorter range, they may become less useful, since their power decrease greatly late game when unit on board become less. I believe they are more effective in threatening than real attack since attacking on highly pack board early game usually mean suicide.

To defend against them, you can either: 1.move away the under threatening unit, 2.move away the unit that work as the material for leaping, or 3. move another unit in between the leaping material and the target of it. For me, it varied the game play.

In the second description, I actually make the higher-tier gain leap-move instead of normal move. Unfortunately, that picture was not save.

It is not that effective against a king since a king is not limited to certain area on board and has quite good mobility.