Greetings! We're gonna talk about parallel universes some mechanics, item usage, and movement! (game breaking not included).
I've got every single achievement from both The Binding of Isaac games by now, and did many full runs as The Lost just for fun (why not?).
Remember: even if you acquired "bad" items on your walkthrough, you can still prove yourself using your knowledge and giving your best. Let's find out!

A common trick where you can pass through their corners without taking damage.

TNT blocks can be exploded by firing tears at them, right? Welp, if you shoot at its corners like the GIF below, they will explode too.
This works with other obstacles (fireplace, poop), and enemies too, if they are close enough.

Suture (the little one) and its variants can be locked shooting on a good spot + angle.

Bombs are good, don't forget it. Let me show you how to use them properly:


Try to blow two or more things with the same bomb


Open Red Chests first if there's a Stone Chest too. They can contain Troll Bombs.


A bomb's explosion can carry you any pickup.

This includes chests, which are a little bit harder to move.

Not much to say here. In this specific room, just move quickly and you'll be safe.

An item that teleports you outside the room can be helpful on rooms like Challenge / Super Challenge Room, taking rewards and avoiding fights. pacifist, yay

As you may know, if you gain the ability to fly and enter a Curse Room, the door won't deal you any damage, but when you exit, it does. Use a teleport item inside the room and that's it! Just be careful with the item you choose. *cough cough The Emperor cough Undefined*

NO LONGER WORKS IN REPENTANCE

It can be triggered two times while taking just one instance of damage.

As shown before, chests can be moved, even through corners like the GIF below.
Works with more pickups like trinkets and hearts (if you can't pick any).

That's it for now. I may add more tips in the future. Any critique is welcome :)
Many thanks to MoistAndDelicious for her grammar skills.
Hope this helps and makes you enjoy this fantastic game even more. Farewell!