Do you get access to a summoned creature's special attacks/spells with "Summon Nature's Ally"?

Question

The Summon Nature's Ally spell mentions:

This spell summons a natural creature. It appears where you designate and acts immediately, on your turn. It attacks your opponents to the best of its ability. If you can communicate with the creature, you can direct it not to attack, to attack particular enemies, or to perform other actions.

A summoned monster cannot summon or otherwise conjure another creature, nor can it use any teleportation or planar travel abilities. Creatures cannot be summoned into an environment that cannot support them. For instance, a porpoise may only be summoned in an aquatic environment.

The spell conjures one of the creatures from the 1st-level list on the accompanying Summon Nature’s Ally table. You choose which kind of creature to summon, and you can change that choice each time you cast the spell. All the creatures on the table are neutral unless otherwise noted.

As a 7th level druid you get access to "Summon Nature's Ally IV" which gives you access to creatures like the Unicorn. A Unicorn comes with interesting qualities such as:

Darkvision 60 ft., magic circle against evil, spell-like abilities, immunity to poison, charm, and compulsion, low-light vision, scent, wild empathy

And special attacks such as:

Turn undead 13/day, smite evil, spells

Does this mean a Unicorn that is summoned with Nature's Ally IV has access to these qualities and special attacks and the druid that summoned it can use its special attacks such as turn undead, smite evil and all the spells the unicorn can cast?

Answer 1

The creature has all its abilities, and you can use nearly all

When you summon a creature, you use its normal stat block, including its special attacks. A limitation on ability use is given under the Summoning rules in the introduction on Spells:

A summoned creature cannot use any innate summoning abilities it may have, and it refuses to cast any spells that would cost it XP, or to use any spell-like abilities that would cost XP if they were spells.

So, only if a spell-like ability would cost XP as a spell, or it is a spell that costs XP, or summons a creature itself, it cannot be used. In addition, the spell itself excludes teleportation or planar travel abilities. Everything else is possible.

The text about Conjuration spells also states that

Creatures you conjure usually, but not always, obey your commands.

Unless the spell in question says otherwise, if you can make yourself understood, the summoned creature -- including the unicorn -- will follow your requests to use its special abilities. For unicorns that should be easy, as they speak common.

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P.S. Note that the "Unicorn" entry in the monster manual has two Unicorns, the plain unicorn at CR 3, and the Celestial Charger at CR 13, which has the powers of a 7th level cleric. As Summon Natures Ally IV only allows you to

summon one 4th-level creature, 1d3 3rd-level creatures of the same kind, or 1d4+1 lower-level creatures of the same kind.

you cannot summon the Celestial Charger variant with it. You can only summon a basic unicorn. It still has a lot of useful spell-like abilities, but does not have the turn undead ability.