custom mode is literally z_next = f(z, c).
start from z^2 + c, then add one thing at a time so you can see what changed.
you can use + - * / and ^ (integer powers), plus sin(), cos(), exp(), conj(), abs(), sqr(), inv(), pow().
constants: z, c, i, pi, e. yes, 0.355 + 0.355i works.
t is the animation time (0 → 2π per cycle). try: z^2 + c + 0.3*sin(t)*z or z^2 + c + 0.1*t*i.
if a formula goes weird, roll it back to something small and build back up.
t directly regardless of this setting.t (0→2π) wired into the fractal iterationt directly in your formula (e.g. z^2 + c + 0.3*sin(t)*z) — time genuinely mutates the iteration