Knockback into another creature

[Crucius]

When you push a monster away (repelling blast, thunderous smite, shove, you get the idea) and that would push them into the square of another monster, do they stop being knocked back (as if hitting a wall for example) or are they knocked 'through' the other monster and end up on the other side? (provided there is enough knockback of course).

Today a gargantuan creature was knocked back into a medium creature, and I was unsure how it would interact exactly. Does the difficult terrain clause apply here (if it does, what if the knockback isn't great enough to force the first creature through the second, where does it end up?)? Is the smaller monster knocked back as well? Does the gargantuan monster stop being knocked back as soon as it hits another creature?

(I ruled it as that the gargantuan monster would be knocked back the same as normal, and the smaller monsters would be 'ejected' from their squares to the outside of the bigger monster through the shortest route)

There is a 100% chance that this will happen again (what with the warlock, paladin, telekinetic wizard and artillerist in the party) so next time I want to come prepared.

What's your take on this?

[stoutstien]

Generally if the creatures are 2+ size difference they can move past each other as DT. Forced movement tend to go around DT so all n all no real problem here until they would stop in the same space.

[Gale]

Ah, they really should have put a size limit on Repelling Blast. Regardless, the rules only state that a creature cannot "willingly" end its turn in a creature's space. Forced movement from being shoved is not willing, and therefore a creature can technically share a space with another creature if they have been shoved into that space. At least, that's my interpretation.

I think a house rule here is probably better though, as otherwise it can create some issues. For example, a hobgoblin standing in a 5 ft. wide doorway, is effectively blocking that way of entry and exit to any other creature. However, if you can shove a creature into that hobgoblin's space, then you could shove a willing ally into the hobgoblin's space, that ally can then move right past them, and there is nothing the hobgoblin can do about it. (Other than potentially make an opportunity attack.) This isn't game breaking by any means. But it's an example of how the rules as written can result in a silly, undesirable scenario.

If I were DM, I'd likely make a house rule that if you attempt to shove a creature into a space that they cannot willingly end their move in, then the forced movement is stopped immediately. You can however, shove a target through another creature's space; as long as the total movement doesn't leave the target inside a space that violates the previous rule.

This prevents me from having to awkwardly stack monsters on top of each other, and I don't have to deal with the logistics and consequences of creatures occupying the same space through a loop hole. It might be tempting to let players knock enemy's prone by shoving another creature into them. But that's obviously too powerful to allow, especially given how easy it can be to shove a creature.

[Vogie]

Personally, I do the exact opposite of the above two posters.

I try to make my encounters as cinematic as possible - So when stuff gets moved, there's an impact. If two creatures collide due to forced movement, I treat it like a fall into a creature - they take the fall damage, but divided between them. If a Larger creature moves through a smaller creature, there's usually Saves involved.

If the smaller creature would have just caught the side of the moved creature, that's a Dex Save to dive out of the way or be impacted (take damage, knocked prone)
If the smaller creature would've been impacted by the moved larger creature dead-on, then it's usually a STR Save to either keep your footing and be slid along with it, or be trampled or otherwise impacted (Damaged, knocked prone, restrained under the larger creature).
My players simply love it. They strive to push things around, knock them off of things, and whatnot. In the grand scheme of things, it doesn't do a ton of damage, but it does add a bit of verisimilitude to the game, and encourages them to think outside the action list. Grasp of Hadar EB's to yank the target out of the barn's loft, so they not only take Force damage, but bludgeoning when they hit the ground. Air Genasi Barbarian Levitating above the treeline, then doing a rage-fall-attack on their target when that creature wanders out of the treeline (with an acrobatics check at the end to see if they land on their feet or pratfall)

I know it's not RAW. However, it's incredibly fun for both myself and the players