for a hot moment we thought that they'd have negative mass or react negatively (as in, fall up) to gravity but we found out that anti-hydrogen does in fact fall down.
anyways we use antimatter elements in PET scans regularly.
remember E=mc²? yeah that's the rate it explodes at
Anti-elements are fun 'cus they're almost identical, until you strip a lepton or two and suddenly they'll go the opposite way in a magnetic field.
Or they find their counter parts and go "oops! I found my normal matter counter parts and FUCKING ANNIHILATED BOTH OF US IN MUTUALLY ASSURED DESTRUCTION"
Granted, it's more dramatic than it sounds. It happens all the time (I am not kidding, it does).