You've probably perfected it by now but I'm gonna say how I did it anyway. I used Mario, Rabbid Mario and Rabbid Yoshi.

First of all use Marios M Power ability for 70% extra damage. Then team jump onto the first smashers head for 150 damage, land on the top area as far away from the pipe as possible.

Next use Rabbid Yoshi to slide the Smasher, down the pipe, slide the next 2 Smashers, all for 90 damage, down the pipe again to the far corner of the bottom area near the smaller enemies.

Next, use Rabbid Mario, down the first pipe, slide the 2 smashers for 170 damage each (the explosion from hitting one should deal 70 damage to the next one). Down one of the pipes again, the one that Rabbid Yoshi didn't use, into the middle of all the smaller enemies. Use the attract ability and then hammer them all. It should kill all of them.

Back to Mario, shoot the top Smasher and that should kill him.

That's turn one over, with only 2 smashers left. They will probably come up the pipe towards Mario but if you put him in the corner they can't reach him.

Now, using Rabbid Yoshi, back up the pipes until you can slide both smashers, put him in the furthest away corner from Mario.

Then Mario can move right next to them and hammer them both to death.

You should have killed every enemy in two turns and received no damage. You can probably come back later with better weapons and do it better than that, but that's how I did it my first time doing World 4.