mtg arcades commander deck the Strategist Commander MTG Deck Guide: Arcades,

Lightning, Security Sergeant** A perfectly acceptable creature, Lightning, Security Sergeant is a touch smaller than ideal in power, but provides impulse draw and some evasion

An Aura put onto the battlefield this way doesn't target anything (so it could be attached to a permanent with shroud, for example), but the Aura's enchant ability restricts what it can be attached to

Yuna, by contrast, is worth $8

You must still follow all timing restrictions and pay all costs when casting the exiled card

It will also trigger if it became blocking as a result of effect, but only if it was not already declared as blocking (see rule 509.1g)