since there is apparently a possibility that this topic is not completely pointless I guess I will write up a somewhat more constructive post.
I will begin by talking about crawl's uniques and an overarching problem with said uniques. As a whole, crawl's uniques have a huge flaw: they are overwhelmingly not actually worth fighting. The risk-reward is completely out-of-whack. Killing Frederick is by no means impossible. In fact it's not even terribly hard. For doing this, you get a whopping total of a bit less than 3800 xp, and maybe if you are lucky a good weapon (let's be optimistic and say you get a good weapon for your character 20% of the time.)
For comparison, frost giants have noticeably less powerful spells and give about half as much xp; they also have a pretty decent weapon (battleaxe of freezing). They do not come in packs; Frederick does not come with a band. I believe frost giants are typically located deeper in the dungeon than Frederick but this might be not entirely correct. I will assert without proof that it is significantly less dangerous to kill two frost giants than to kill one Frederick. Alternatively, you could compare Frederick to stone giants. It takes about 2.5 stone giants to make one Frederick of xp. This is also signficantly easier than killing one Frederick.
Therefore, why would you ever fight Frederick? This is not a case of making the player make a decision; this is a case of the risk-reward balance being far too skewed toward "risk" and thus Frederick is
too dangerous to be interesting (or, alternatively, he should give much more xp, but then you run into the problem of crawl probably still having more xp than players need ... I'm not going to get too deep into fixing crawl's uniques in this post). Frederick is not a special example; I picked him because he is simple so it is easier for me to compare him to frost giants and stone giants than to compare a unique like Mennas or Nikola or Jorgrun to other monsters. Why do you think the advice given on this forum for dealing with Mennas or Mara is uniformly "don't fight"?
I cannot say for sure that octopode crushers are problematic in a similar way; I have no experience with them. However, I will assert the following two things: melee and ranged attacks are, in general, of similar power levels in crawl. In general, monsters in crawl are not particularly susceptible to melee attacks or to ranged attacks. Now I will suggest this third thing: that octopode crushers are significantly less susceptible to melee attacks than they are to ranged attacks, since they have an ability that specifically throws you away if you get into melee with them. If you believe all three of these are true, then we are in the same situation I just discussed re: Frederick and fight-or-don't-fight. The correct choice is to never melee the monster, since the risk-reward is too skewed. They are
too strong against melee to be interesting.
It is possible that my suggestion that octopode crushers are significantly more dangerous in melee than at range is wrong, and of course my conclusion here relies on a certain degree of "significance". I don't actually care much about this particular monster; this is just to illustrate a point that I find many people (including the devs, based on my conversations with them) sometimes miss when talking about crawl monsters.
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On a different note I would suggest that monster abilities that reposition the player are bad gameplay, and this is my more specific problem with crushers.
I find the most interesting part of crawl tactics to be positioning. Positioning is twofold: it is both the location of your character in relation to the other monsters on the floor (both those in-los and those out-of-los and even the monsters that do not exist but you as the player fear might exist), and the location of your character in relation to the dungeon features on the floor. For the majority of enemies in crawl, the player has very nearly absolute control over both of these two factors (yes, enemies move around, but they do so in an entirely predictable manner for the majority of monsters in crawl). Some enemies play with the first factor of positioning: they move monsters around in a non-predictable manner (most commonly a monster moving itself via blink, but also things like blink allies encircling or convoke). I don't have a problem with this, as long as it is not the norm; there is still skill in positioning yourself in a good location with respect to the static dungeon features. Monster dig plays with the second factor, by actively altering the dungeon around the player. I do not like this much personally, but I do not have a game design argument for eliminating it, so I will just say that it is similar in effect to moving monsters around. In either case there are still interesting aspects of positioning that matter for the player.
Forcibly moving the player around destroys both elements of positioning. The player is moved around in relation to the monsters on the level, and additionally the player is moved around with respect to the dungeon features. If we take this to an extreme--monster teleport other, which places you on a completely random space on the floor--then positioning before the attack is literally useless. You have taken what I find the single most interesting tactical element of crawl and completely eliminated it from the game. Monsters blinking the player or octopode crushers moving the player around are obviously not so extreme, but it should be evident how much less control over positioning the player has, and thus how much less interesting positioning becomes. I do not think this is a good thing for monsters to do.
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An off-topic exposition on constriction below, though I do not expect changes here:
Constriction is bad primarily because it is a melee effect. There are three important cases to consider:
1) The player is faster than the monster
2) The player is the same speed as the monster
3) The player is slower than the monster
I will begin with 3)
In this situation the player cannot outrun the monster without using consumables (if the player has haste spell and using said spell makes the player faster then you can either consider the MP used as the consumable, or you can consider this case 1), whichever you prefer), so constriction limiting player movement has little effect. It may block a blink, but mainly this only matters if the player tries to blink after getting constricted, which is easily avoidable. By and large the effect is just increased damage for the monster and slightly increased HP for the monster (since the player will want to spend turns moving to break constriction instead of attacking, most likely).
Now situation 1)
In this situation the player can outrun the monster without consumables. Constriction is only ever important here in concert with other monsters. However, since the constricting monster itself is slow, the player can, tediously, separate it from any monsters of different speed with little danger. So let's just assume that all the monsters the player is dealing with are slow. Since this is a melee effect, one possibility is you actually end up in a situation like the octopode crusher one above, where you just aren't supposed to melee constrictors. I have the same problems with it here that I did above. If meleeing the monster is still fine, then in practice constriction just ends up being extra damage. You can reposition into hallways if you like (digging exists) so being stuck next to other, non-constricting monsters is not really a thing.
Situation 2) is actually the most troublesome, because of quirks about how constriction works.
In this case, if you just stand and fight the monster, then constriction mostly just acts as more damage for the contrictor (and more HP if the player spends moves trying to break it). The problem here is that, paradoxically, constrictors are actually easier to escape once they move next to you than monsters that do not constrict. You see, when the player breaks constriction, the constrictor is stunned for a short time. This means that if you somehow end up next to a constrictor but want to escape, the best plan is to purposely get constricted, break constriction, and then run away. Even if the end result of this is not undesirable (I would say it is, but will not prove it) the fact that it is counterintuitive is problematic.
So in the end my conclusion is that all constriction does is 1) add damage/hp to the constrictor and very occasionally 2) block blinks (note it does nothing to teleports). If 2) is a thing worth having, why not have that be its own thing completely? If you want to affect player movement, then having it done via a ranged ability (nets, barbs) is substantially better than doing so via a melee ability, since cases 1) and 2) are very different.