/f/ shit

// So you probably have something like this already
const sprite_list = [...];
const message_list = [...];

function draw_warning() {
    var sprite_new = random(0,sprite_list.length);
    var message_new = random(0, message_list.length);

    display_sprite(sprite_list[sprite_new]);
    display_message(message_list[message_new]);
}

// But with a few tweaks...
const sprite_list = [...];
const message_list = [...];
var sprite_prev; // A global var; it'll stick around between invocations of draw_warning(), so the program'll remember what combination showed up last
var message_prev;

function draw_warning() {
    var sprite_new;
    do {
        sprite_new = random(0, sprite_list.length);
    } while (sprite_new == sprite_prev); // Read: if it's the same sprite as last time, get a new one.

    var message_new;
    do {
        message_new = random(0, message_list.length); // actionscript needs macros tbh
    } while (message_new == message_prev);

    display_sprite(sprite_list[sprite_new]);
    display_message(message_list[message_new]);

    sprite_prev = sprite_new; // Remember the sprites from this time for next time
    message_prev = message_new;
}