1)Problems that could arise if a hacked Pokemon enters the game
2)glitches in black and white.
Crashing, freezing, glitching, appearance of bad eggs, not being able to battle with hacked Pokemon, parts of the game being inaccessible, and sometimes ultimately having to restart your entire game.
List of glitches in Gen V
List of Berries - while this a Gen IV list, it hasn't changed since then and all of those berries are present in Gen V. Some aren't obtainable, but are still seen rarely (e.g., Enigma Berry is found as a Battle Subway NPC partner's occasional held item).
There are two main "glitches" in black and white (that is not counting the subway partners Pokemon holding berries that you are unable to get in the game) the glitch ---- - which is basically missingno in b/w and b/w 2 and the bad egg which has been infamous since generation three when eggs were introduced (the bad egg to punish hackers) but Marzipan basically gave you the main amount of glitches from generation five so those are what I have.