The Dink Network

The brain 12 sprite will delete itself after it reaches the target size, and sp_seq will return -1 for deleted sprites, so you should check if the seq > 0.
Also make sure that the script is not attached to the explosion itself, or it will be killed with the explosion.

Try this:

int &seq;

sp_timing(&current_sprite, 1);

loop:
&seq = sp_seq(&explosion, -1);
if(&seq > 0)
{
	move_stop(&current_sprite, 2, -2147483648, 1);
	goto loop;
}
//Sprite done animating

edit: had the check wrong: <= instead of >