Possibly a cursed item that is apparently enchanted to secure big wins, and indeed does so, but goes off immediately after helping its owner to a major haul; or possibly a nasty weapon to be used by a gambler who doesn’t like the way the game is going, the cardsharp’s reversal is a deck of cards where the aces of each suit are modified in such a way that the edges can become razor-sharp mid-shuffle, and the cards themselves a little larger and substantially heavier – perhaps they even transform into slightly-larger-than-card-sized razors.
In PFRPG terms, this transformation triggers a Reflex save vs DC 25. On a successful save, the victim takes 2d6 damage plus 1d6 bleed, and a -2 penalty on all Dexterity- based checks involving the hands until the previous damage is healed. On a failed save, the target loses 1d6 fingers: in addition to the above effects, for each finger lost there is a further permanent -1 penalty to the aforementioned checks and to checks pertaining to grip strength (eg disarm checks) until the fingers can be reattached, regrown or replaced, presumably with a regeneration spell or similar. This penalty reduces by 1 for each level gained, as the character learns to compensate, but never to less than half its original value, rounded up. A hand that has lost enough digits may lose the ability to grip altogether.
When the chain or rope to which this anchor is connected reaches its full extension, both the anchor and the chain/rope become completely immovable and nigh indestructible, like an immovable rod (only even stronger). It cannot be raised. Attempts to damage the chain either damage the objects used to make them, or potentially damage the part of the ship nearby as weapons bounce off. Additionally, the natural movement of the ship on the sea will grind it against the chain like a thin rock, causing the ship to sink eventually. (Use your system’s rules for running aground on jagged rocks to determine damage etc.)
If this is not an intentional trap or cursed item, but rather a misguided invention or a device intended for a more durable ship, it may be possible to deactivate the anchor – but this may require diving down to the anchor and working underwater.
This belt consists of a normal belt buckle and a normal belt end, firmly attached to magically sharp wires (or monofilaments in a scifi game) which then have the middle section of the belt sewn around them. When the belt is pulled tight prior to buckling, the viciously sharp strands slice through first their sheathing and then the victim’s body with so little resistance that the victim is likely to suspect that the belt has broken before they realise the terrible wounds they have received.
These belts are commonly designed to look like potent magical/tech items, and the wealthier sadist will even go so far as to make the belt and then apply genuine enchantments or tech to ensure that it gets worn. Failing that, they are usually of exceptional quality and/or a fashionable make, to snare dandies.
The same basic mechanism can be applied to chokers, ties on sweatpants, sandal straps, corsets – anything that loops around a part of the character’s body and gets drawn tight against what it encircles.
In the PFRPG ruleset, a CR 10 version of this trap would have a DC 27 Perception check to notice the trap, and it would deal 12d6 damage when tightened. You might prefer to vary this to (10+Str mod)d6 – particularly cruel on a trapped Belt of Giant Strength.