Ok, so the solo Thin Lizzy thing is perhaps a terrible idea, but for those guitarists among you that want to expand their sound and add layers of harmony to their guitar lines, a pitch shift pedal is a great way to go.
These creative pedals allow you to harmonise with yourself without the need for another guitarist. Similar to an octave pedal, a pitch shift pedal enables you to split your signal and shift the pitch of one of them. When mixed back together, your wet and dry signals should create the perfect harmony.
Whereas an octave pedal only allows you to jump incrementally in eight-note steps, a pitch shift pedal gives you a different set of options. You can control the transposing of notes in different increments, achieving harmonious major - or minor - 3rd’s and 5ths or even get experimental with some crazy 6ths! Some pitch shift pedals also offer control over pitch bends, alternative tunings, and multi-layered harmonies.
So, no need to keep that annoying 2nd guitarist in the band now - sack him, grab your pitch shift pedal, and noodle away with his stompbox-format replacement to your heart's content.