This is the song in Level 20: Gotcha! and 26 The Abondoned Mines.
G|---------------------------------------------------------------------------|
D|---------------------------------------------------------------------------|
A|---------------------------------------------------------------------------|
E|--0-3-3-3-3-4--------------------------------------------------------------|
then take it up a string
G|---------------------------------------------------------------------------|
D|---------------------------------------------------------------------------|
A|--0-3-3-3-3-4-------------------------------------------------------------|
E|---------------------------------------------------------------------------|
then back down
G|---------------------------------------------------------------------------|
D|---------------------------------------------------------------------------|
A|---------------------------------------------------------------------------|
E|--0-3-3-3-3-4--------------------------------------------------------------|
then up
G|---------------------------------------------------------------------------|
D|---------------------------------------------------------------------------|
A|--0-3-3-3-3-4-------------------------------------------------------------|
E|---------------------------------------------------------------------------|
then up one more string
G|---------------------------------------------------------------------------|
D|--0-3-3-3-3-4-------------------------------------------------------------|
A|---------------------------------------------------------------------------|
E|---------------------------------------------------------------------------|
then back down and down again.
thats the bassline its very simple.