Well:
30Maximized fireballs apparently do it, so how about:
Being a choker (or turning into one with shapechange)
1 Twinned Repeating quickened greater arcane fusion containing one twinned repeating maximized fireball, and one twinned repeating arcane fusion containing one hail of stone and one twinned repeating maximized fireball. That's 10 fireballs.
1 Twinned Repeating greater arcane fusion containing one twinned repeating maximized fireball, and one twinned repeating arcane fusion containing one hail of stone and one twinned repeating maximized fireball. That's 10 fireballs.
1 Twinned Repeating greater arcane fusion containing one twinned repeating maximized fireball, and one twinned repeating arcane fusion containing one hail of stone and one twinned repeating maximized fireball. That's 10 fireballs.
30 maximized fireballs if I can count, if not, everything will repeat itself and cause more damage.
Now to hope the earth doesn't have immunity to fire.