What are some creative ways you or your players have used spells?

Recently, a player was possessed by a ghost. I (Wizard in an OSR) used polymorph other and turned him into a snail and just waited. then I threatened to get a bottle to put it in...and he released the body and we killed the ghost. 

Same OSR wizard but early in campaign (level 1), we entered a tavern and a giant was wedged behind a table and had been for months. he didn't remember how he got there but the tavern was getting tired of feeding him and the giant was taking attribute damage. Told him in Giant (language) that I'd come back for him in 8 hours. Came back with enlarge memorized and reversed it. He had to run up the stairs before it wore off and the ran through the tore (broke it) before it wore off. This was the desert so the environment came in but we wound up with a giant crewmember for a few months till he died). He had to sleep on deck of skyship covered in tarps. The DM had not considered that we could save the giant. 

Lightning lure and thorn whip can be used by flying players (owlin, fairy, etc) ... to fly above a target and cast the spell. If it works, the target gets pulled up, takes damage, then fall damage, then maybe winds up prone. 

We were interrogating someone who kept getting assassinated and I (Druid) kept bringing her back (Revivify) to finish the interrogation. I Also revivified or reincarnated crewmembers (spelljammer this time) to see what was killing them (succubus).

5e 2024 rules I had a halfling druid riding a hyena or vulture familiar. 

As wizard (5E), I used spells to do rogue-like things. I set up some cantrip based illusions with stage props (this was a performance) to make it look like i turned invisible (I did) and was walking into the crowd (I wasn't but they could hear my footsteps (minor illusion) among them) ... so that I could steal something in the storeroom behind the stage.

I've used Create Water to create rain in a dry area to reveal the position of someone in a Cloak of Invisibility. The dry spot showed their current location. The only DM buy-in required was that rain would do that whether magical or not.

Oh, that/s something you do in the game Divinity Original Sin 1 when an invisible enemy attacks. You cast the "rain" spell and you know where he is. they also have a spell that is lie Grease, that works too. 

I've also heard of people throwing sacks of flour around. :)

Launched a fireball up in the air to cast a brief instant of light that revealed an army sneaking toward a bridge. Because of that, the DM had to rewrite some things and a city that was meant to fall was saved.