Spadefish

One species in three tiers: the Spadefish (Chaetodipterus faber). Juveniles are small, dark and disc-shaped, and they drift at an angle like a piece of dead leaf, which is exactly what they are imitating. Adults trade that for a tall silver body with dark bars and a habit of schooling in open water.

The honest problem is scale. The juvenile you buy is a placeholder for an adult that will need a very large system, and a fish this tall runs out of headroom before it runs out of length. Buy one only if the tank it ends up in already exists. If it does not yet, ask me first.