For every 10 levels you complete in the Pit of 100 Trials, you'll earn a new badge or other item:

Effect - Code

Bump Attack Badge - Complete levels 71-80
Double Dip Badge - Complete levels 51-60
Double Dip P Badge - Complete levels 61-70
Fire Drive Badge - Complete levels 11-20
Lucky Day Badge - Complete levels 81-90
Pity Flower Badge - Complete levels 31-40
Return Postage Badge - Complete levels 91-100
Strange Sack (doubles inventory space) - Complete levels 41-50
Sleepy Stomp Badge - Complete levels 1-10
Zap Tap Badge - Complete levels 21-30