The Binding of Isaac

- There's an item on every floor in a special room marked by a crown on the map and a yellow border around the door, but on every floor besides the first it's locked. Always have at least one key to open that room.

- There's a secret room on every floor. A couple items will tell you where it is and you can find it by bombing walls. There's a pattern to where it spawns, though - it can only spawn in a 'blank' map tile with at least 3 rooms touching it (except occasionally on the first floor where there sometimes are no such groupings of rooms)

- There are some rocks that are suspiciously dark-grey. Bomb them for goodies.

- When an item says it "appeared in the basement" that just means it will now spawn (some items you have to do particular things before they'll spawn); it doesn't necessarily mean that they're somewhere in your current game