How do I get around black, square blocks?
Solution 1:
You need to have an item that grants flight.
The list of items which grant permanent flight from the original game is:
- Lord Of The Pit
- Transcendence
- A Pony / White Pony
- Holy Grail
- Fate
- Spirit Of The Night
- Dead Dove
- Guppy or Lord of Flies (collecting 3 Guppy items or 3 "flies" items in one playthrough will give Isaac permanent flight)
- The Hanged Man (Tarot Card)
There are probably several more in Rebirth.
Solution 2:
You can also clip through the blocks with two bombs.