The Dink Network

That should be easy to do.

For each level, you could make a savegame. Then you could have a level selection screen that loads the savegame number of each level (use game_exist() to see which ones are unlocked thus far.)

For checkpoints, you could have a few variables for x,y, and map. Just spawn Dink there in the dinfo.c script. I actually did something like this to keep the annoying die menu away.

void die ()
{
  if (sp_brain(1,-1) != 1)
  return;
//scream! 
//not loaded in your start.c btw
//load_sound("wscream.wav", 12);
playsound(12, 21050, 0, 0, 0);
script_attach(1000);
sp_brain(1,0);
wait(1500);
&player_map = &chk_map;
load_screen();
draw_screen();  
sp_x(1, &chk_x);
sp_y(1, &chk_y);

  int &explo = create_sprite(180,250,7,167,1);
  sp_seq(&explo,167);
playsound(24, 21050, 0, 0, 0);

&life = &lifemax;
sp_brain(1,1);
dink_can_walk_off_screen(0);
kill_this_task();
}