Introduced new mechanic Creep.pull. It allows one creep to pull another creep helping it to follow:

creep1.pull(creep2); // first creep requests pulling
creep2.move(creep1); // second creep accepts it

creep1.move(RIGHT); // actual move

Here creep1 will gain fatigue for both creeps. creep2 may not even have any MOVE body parts. Creeps may belong to different players. Creep.pull can be called recursively by multiple creeps in series. Thus, a fully XZHO2-boosted 50xMOVE "train" can pull several 50xCARRY creeps just on its own.

PTR Documentation

Commit engine#4d37717

Other unrelated changes

• Containers now can be built next to exit tiles (engine#a44e238).
• Hostile creeps don't block building in safe moded rooms (engine#3d21e7c).
• Various fixes.

IMO, this feature should result in only the lead creep being charged for a single const CPU call, allowing it to be useful to save CPU for long cargo trains with boosts (as a 50 boosted move engine could haul 200 boosted carry parts with 200 capacity each, for 40000 total carry capacity).

3 const calls

.pull() is free.

Those seem much more useful and interesting.

Can I ask why this is not creep.pull(target); creep.move(destination) or creep.pull(target,direction)?

Those seem much more useful and interesting.

Did you miss the part about it being usable on other players creeps, and them having to accept it? Or am I missing where you included that in your post?

1. You have more move than them. If you try force (unwilling) them with pull, you move them but get fatigue equal to your net move advantage (your move - their move). AKA if you had 20 move they had 10, you get to move them, but get fatigue as if you only had 10 move parts.
2. You have less move than them. Can't pull unwillingly, could maybe slow them down at cost of your fatigue?
3. You have more or less move than them, and they accept it willingly. You move them.

What happens to the fatigue gain of the pulling creep when the pulled creep has move parts? Do they contribute to reducing fatigue gain?

When several creeps trying to move onto the same tile, the priorities are: creep having follower, creep that being pulled, creep that pulls someone, creep with best moves/weight ratio

@davaned That may be interesting, but the current implementation is not supposed to be used unwillingly.

@smokeman When several creeps trying to move onto the same tile creep that being pulled takes priority.

@obamallama No, creep pulling another creep receives another creep's fatigue. Pulled creeps, however, can use his MOVE parts to reduce the fatigue he already has.

How does it handle switching rooms? I can imagine the train creep being knocked into the next room while the pulled creep is still 1 tile in front of the exit

When several creeps trying to move onto the same tile, the priorities are: creep having follower, creep that being pulled, creep that pulls someone, creep with best moves/weight ratio

Does this mean we can use Creep.pull() to prevent other creeps from squeezing in-between attacker-healer pair creeps? Assuming attacker pull()s the healer along?