Divine Assistance

Sometimes the hero can't save the day alone. That's where gods come in.

In Greek mythology, gods would often give heroes gifts that would help them on their quest, or simply have fun by making the hero suffer. The main reasons a god will help the protagonist is either because the fate of the world depends on it of because the character has or can get something they want. The god may physically come with the hero on the quest or give them a few "helpful" items.

Since it would be too easy to complete a quest with a god's help, whether they are being genuinely nice or playing prank, their help usually just makes things more complicated.

Note that this is different from Deus Ex Machina. This is a more specific trope.

Examples of Divine Assistance include:

Anime and Manga

Pokémon has Uxie, Mesprit, and Azelf helping Ash, Pikachu, and Co. during the Diamond and Pearl arc, and Reshiram and Zekrom helping them during the Best Wishes arc.

Film

God himself appears to the eponymous characters in Bruce Almighty and its sequel, Evan Almighty.
Clash of the Titans (1981). Zeus interferes repeatedly to help his son Perseus and punish those who oppose him. He also has other deities give him divine gifts, including a shield, a sword, and a helm that grants the power of invisibility. The goddess Thetis likewise tries to help her son Calibos but it doesn't turn out very well.
Jason and the Argonauts (1963). The goddess Hera is allowed to help Jason five times during his adventures. Jason also uses an amulet he receives from Phineas to get help from the god Triton (Poseidon's son).
Xanadu. An Olympian Muse named Kira (actually Terpsichore) inspires two men to artistic greatness: one in the Backstory and one in the present.

Literature

In The Secrets of the Immortal Nicholas Flamel, a the Elders Scatatch journeys along with the Flamels and the Newmans, and they occasionally get help from Elders such as Areop-Enap and Prometheus.
The Kane Chronicles has Egyptian gods, including Horus and Isis, inhabit the main character's bodies as hosts. Others, such as Bast and Bes, escort the heroes along their quest.
Towards the end of The Colour of Magic, The Lady intervenes to help Rincewind and Twoflower escape Krull.
In Michael Moorcock's novel Elric of Melnibone, Elric is saved from drowning by the elemental deity Straasha.

Oral Tradition, Folklore, Myths and Legends

The Odyssey: Several gods show up to either help or screw over Odysseus while on his journey.
Perseus got some help from some of the twelve Labours of Hercules, most notably in his slaying of the gorgon Medusa.
In most religions' bibles, God talks to prophets and gives them visions of the future, among other things.

Tabletop Games

Dungeons & Dragons:
- The 1E Dungeon Master's Guide had game mechanics for divine intervention - a specific percentage chance that a character's deity would intervene in a crisis situation and aid them.
- At the end of module Q1 Queen of the Demonweb Pits, the PCs deities saved them from the destruction caused by Lolth's death.
- Module T1-4 The Temple of Elemental Evil. The deities Iuz the Old and St. Cuthbert of the Cudgel can appear under certain conditions. If they both appear, Iuz will restore all of his dead leaders to life and St. Cuthbert will do the same for fallen PCs.
- The 2E Al-Qadim campaign setting allowed Fate to help or even save player characters in great danger.
1E Stormbringer
- PCs received Elan for various actions. If a d100 roll was less than the PC's current Elan, their deity would save them.
- Adventure Stealer of Souls. If Tormiel can get a message to the priests of Lassa, they can petition Lassa for divine intervention to help him. It could take the form of a powerful air elemental or a breeze that puts everyone in the house to sleep.

Theatre

A Midsummer Night's Dream. Oberon tells Puck to make Demetrius fall in love with Helena, but Puck ends up making Lysander fall in love with Helena instead. Then Puck completes his task so that Demetrius and Lysander are fighting over Helena, Hermia is completely confused, and Helena thinks that all three are mocking her.

Video Games

Drawn to Life has you play as "the Creator", creating and guiding the main character throughout the game.
In Nethack, the #pray extended command lets you ask your god for help. The nature of the help—if indeed the god decides to help you at all—depends on the nature of the trouble and how pleased the god is with you. Worth noting, if your god is sufficiently pleased with you, prayer will have a positive effect (possibly including a gift) even if you're in no trouble at all.
Super Mario Galaxy has Rosalina help Mario on his quest to save both Peach and the cosmos from Bowser. Rosalina is humanoid but has acquired magical powers.