Yes, it does break the grapple (if you end up outside of its reach)
a creature takes 2d8 thunder damage and is pushed 10 feet away from you
Shoving uses a similar wording:
If you win the contest, you either knock the target prone or push it 5 feet away from you
Assuming you opponent only has a reach of 5 foot (and did not start in your space), shoving should fulfill the clause in the Grappled condition in the same way as Thunderwave would:
The condition also ends if an effect removes the grappled creature from the reach of the grappler or grappling effect, such as when a creature is hurled away by the thunderwave spell.
It's fine if a third party does the shoving (assuming they can shove in the right direction). The above quote does not state that the grappled creature must cause the effect, only that the effect must remove "the grappled creature from the reach of the grappler or grappling effect".
Also note, moving either the grappler or the grappled creature can count as an effect that "removes the grappled creature from the reach of the grappler or grappling effect"
(i.e. in the same way that you can remove someone from danger by eliminating the danger instead of actually moving them). Also see this answer here about the graplee taking the shoving action.
In the querent's diagram, if the character taking shoving action pushed the Crocodile down and to the left (which is technically also 'away' from himself, but check with your DM), it should be enough to separate the two opponents (assuming you are using a grid and/or don't charge extra for the diagonal movement - again, check with your DM)
No, otherwise it would be mentioned by the spells' descriptions.
That being said, I believe the reason why it's not mentioned are the spells' intended usages / their themes.
Lesser Restoration allows you to remove the following conditions:
disease, [...] blinded, deafened, paralyzed, or poisoned
All of them are physical conditions, leading me to believe that the intent of the spell is to be your all-rounder spell for minor illnesses etc. Frightened is not a physical condition, therefore it doesn't fit the theme.
Moving on to Greater Restoration, it can remove the following effects:
- One level of exhaustion
- One effect that charmed or petrified the target
- One curse, including the target’s attunement to a cursed magic item
- Any reduction to one of the target’s ability scores
- One effect reducing the target’s hit point maximum
It removes major detrimental effects, and once again, they are all physical effects (and curses), aside from the Charmed condition. In my opinion, it would be reasonable to include Frightened alongside Charmed, but since Charmed can be way more impactful than being Frightened (in one case, you run away, in the other, you might fight for the opposing team), that's probably why they chose Charmed instead of Frightened.
In addition to the previous paragraphs, there are spells that do help against the Frightened condition (sometimes limited to against specific types), just not the Restoration spells:
- Protection from Evil and Good: immune against being Frightened (and other effects) by aberrations, celestials, elementals, fey, fiends, and undead, and advantage on saving throws for existing effects.
- Aura of Purity: advantage on saves against Frightened (and other effects)
- Heroism: immunity against the Frightened condition
- Heroes Feast: immunity against the Frightened condition
- Calm Emotions: can suppress the Frightened condition for its duration, i.e. up to 1 minute. Effect resumes afterwards, unless the duration has run out.
There are probably a few others that I failed to find.
Depends on how they're restrained.
Since you've clarified that the creature is trapped in the coils of a giant snake, no, they won't get released. Repelling Blast throws the snake backward; this won't untangle whatever is wrapped up in it.
But the Grappled condition says...
Yes, I know. Here's the thing: All that rule says is a creature can't continue grappling another creature that's out of reach. It's still up to the DM's judgment whether the snake in fact moves out of reach of its victim. It's perfectly consistent with the rules for the snake and whoever it's grappling to get pushed as a unit.
Repelling Blast says that it pushes its target 10 feet back. This is not absolute. If the target is standing in front of a stone wall, I don't know a DM anywhere who would rule that they're pushed right through the wall, even though the invocation doesn't say "10 feet, or until it hits something solid".
Now replace that stone wall with another creature. Does the target stop moving when they hit a stone golem? An elephant? A dog? A stirge? At some point the answer is going to change from "probably yes" to "probably no, and the other creature either gets pushed with it, or moves out of the way".
Now, what happens when it can't move out of the way? Suppose the target is roped to another guy. There has to be a point of failure somewhere: either the target doesn't move, or the other guy moves with it, or the rope breaks. Repelling Blast doesn't say it moves other creatures, but it also doesn't say it breaks ropes, so the DM will need to rule on where the system stops behaving ideally.
In this case, the snake is the rope, and snapping it in half so that the constricted creature can escape is a pretty drastic (and abusable!) outcome for a 10-foot knockback. More reasonably, a DM would decide that either the snake doesn't move, or it brings its victim with it.