Use Giant Fly to drag an enemy over a Bonfire?

Quote from MongooseGef >>

Quote from SunIsGettingRealLow96589 >>

Or use a normal familiar with a bag of holding with 500 pounds of boulders

 A valid plan! I only have one bag of holding right now and it’s holding a lot of my party’s loot, but absolutely a valid play. Though it may need to be a “replicate magic item” bag of holding created by an artificer. That would allow them to dispel the magic instantly, causing all the boulders to appear in a space at once. Otherwise the GM might force the familiar to remove the boulders from the bag one at a time 🤣

If you want to do this and avoid borderline rule interpretations, play an artificer.  At level 5 you get the homunculus spell, which is mostly like a mechanical familiar, but it has no restrictions against attacking.  It actually has a built in weapon that does force damage. You can then have it use a bag of holding to drop boulders or whatever. 

As long as the boulders are 2ft in diameter or smalller, you can dump them out as a single action. The utilize action can turn the bag inside out and everything falls out.

And as an artificer, you can make your own bag of holding after a long rest.

 And if boulders are hard to come by, use tinkers magic to fill it with caltrops.

I would not allow the spell to summon a giant fly in the first place. Its supposed to be a small creature around large cat sized or smaller. RAI.

Allowing it to carry around characters would violate the RAI idea.

the Dm could just say that the original spell failed but the friendly fly showed up instead. Now its dead and can't come back because it was not created/summoned by the spell.

But thats just my opinion.