Its ETB trigger helps you find key cards if youre going for a combo
Usually, the cycling effect created a smaller "cantrip" version of the spell
If you somehow don't win, you can Xyz the other Diablo and shuffle your banished zone into the Deck (effectively canceling out any cost you intended "banish half your Deck" to even be)
It deals 2 damage to players if they have 5 or less life, which is an interesting idea, but it hits both players and is too expensive
Then, by the time you can do the -10 ability, a mana sink or expensive spell is a great way to end a game
120 HP may seem little, but with Eviolite and Resistance, this skyrockets to 160, and Special Metal jacks it up to a maximum of 200