How to push updates into Kirby/Other characters (originally by Archytas):

1. In update.gml along with copying the attack values to the enemy kirby, set an arbitrary value in an unused window for checking later. For example:
set_window_value(AT_EXTRA_3, 2, AG_WINDOW_ANIM_FRAMES, 'value');

2. In whatever script you want to have kirby run:

if enemykirby != undefined { //if kirby is in a match & has swallowed the character
with oPlayer { //Run through all players
if (get_window_value(AT_EXTRA_3,2,AG_WINDOW_ANIM_FRAMES) == 'value') { //Arbitrary value in an unused window
//your code here
}
}
}

3. To simulate attack_update, use this in update.gml:

if enemykirby != undefined { //if kirby is in a match & swallowed
with oPlayer { //Run through all players
if ((state == PS_ATTACK_AIR || state == PS_ATTACK_GROUND) && attack == AT_EXTRA_3) {
//your code here
}
}
}

Kirby also looks for a custom copy ability icon by sending "newicon" over, for example:

var myicon = sprite_get("kirby_icon")
with enemykirby {
newicon = myicon
}