It appears as two humanoid figures, one male and one female, horrifically fused together and tied with a series of bondage gear and straps.
The male side is the side that will attack Alex Shepherd, and his muscular arms are morphed into huge, club-like appendages much like those of the Closer and Mandarin monsters from previous games. He also appears to be wearing some sort of chest armor and he wears boots.
The female is fused into the male's back, with her hands tied above her head and thereby the male's as well, while her feet dangle freely behind. She wears extremely high unwalkable stilettos.
The male and female's wrists being tied together make up the Siam's "mouth", which highly resembles the star-nosed mole.
The male's enormous arms prevent the monster from walking on two legs, rendering the monster a quadrupedal which walks on all fours like an animal.
The Siam's movements are ape-like. The creatures deal heavy damage with their arms and are surprisingly swift for a creature of its size, especially when the beast is running in quick bouts; this is when it can cause some of the most devastating damage to Alex, taking him by surprise and knocking him over. They will also try to pummel Alex while on the ground, so it is wise to stay out of their large striking range. Movement while killing a Siam in close range is usually mandatory, considering they are resilient and therefore act barely even affected by gunfire and will continue to dash at Alex, each shot only mildly stalling them. The female side is significantly weaker than the male side, and damage is increased when attacking her.
The best and safest way to defeat a Siam is to use a high-strength firearm such as the shotgun while backing away and evading as necessary. When forced to fight at close range or just to conserve ammo, dodge as much as possible and position Alex behind the monster, looking for an opportunity to attack the female side with continuous heavy axe strikes. If the player is able to stun the Siam with a heavy strike, it becomes vulnerable to an easy one-hit kill. The Siam will run away every so often, giving a prime opportunity for use of a firearm at its female side.
Helplessness and fate
The Siam may represent helplessness and being dragged along by fate, and Alex's confusion about relationships. The female is helplessly bound to the male and dragged around with him, much as Alex Shepherd himself has been bound by his family birthright; in Alex's diary, he writes, "...it sucks to have the town named after some great-great grandfather of yours." almost as if he finds his family embarrassing or shameful.
Lillian and Adam
Additionally, the female form may represent the powerlessness of Alex's mother. His father made all of the decisions, and she was forced along with it, agreeing with him despite her own feelings. This can also be supported by how the female voices a gasping, painful noise in combat that is primarily overpowered by the male's growling, domineering sounds.
Women as a burden (Elle/Lillian)
The female side may be symbolic of how the women in Alex's life could be viewed as a burden to him, whether it be emotionally or physically. In the case of Homecoming, Alex has to worry about his near-catatonic mother and missing best friend, thus Lillian and Elle Holloway are "burdens" to Alex.
Alex and Elle's relationship
Siams always appear when Elle is in trouble or missing, which perhaps accentuates the bonded feeling between her and Alex, that Alex doesn't want to leave Elle because harm might come to her if he does not protect her, as indeed it does, or it may just represent Alex's desire to be close to Elle, both physically and mentally, or perhaps even desiring to touch her sexually, as sexuality is a reoccurring theme in Homecoming. If so, the female part of Siam represents Elle, and the male part represents Alex, and the bonding of these two represents the emotional/romantic bond between Alex and Elle.
The Siam as Elle's monster
It can also be theorized that Siam symbolizes unrequited love and is Elle's monster, not Alex's. When Elle is searching for the missing children, hanging up posters and doing her best to find them, she's exhausted, and feeling more than a little ineffective and helpless, and is unable to convince others to help, especially after people start going missing. When Alex returns, he's also looking for the kids, except he's made a bit of progress in looking for his missing brother, and he's got a couple of leads. Since Alex has these major developments, she may have started to view Alex as the only one capable of moving things along. Some view it as Alex doing the grunt work and Elle following him, unable to do everything he did. It is possible Elle develops a sort of crush on Alex, who's taking charge and running forward, while she lags behind, slowing him down as his 'weak spot'. The Siam could represent codependence, representing Elle's own feelings of helplessness in an overwhelming situation, and therefore relying on Alex, who seems to be the only one who understands and wants to do something about it.
James and Mary
The Siam's appearance can also be representative of James Sunderland and Mary Shepherd-Sunderland from Silent Hill 2. The monster's bondage-like appearance and the male side's aggression alludes to the sexual frustration felt by James. The configuration of the two sides can also refer to James "carrying" Mary, whether it means carrying the guilt of his crime or the burden of caring for her. Defeating a Siam gains the "Shades of James" achievement on the Xbox 360 version of the game, which makes the connection more apparent. One theory is that Siam actually is James and Mary (especially if the "In Water" ending is canon), like the Twin Victim. However, it may be more likely that James became Pyramid Head due to the different appearance of Pyramid Head after Silent Hill 2. James may have become Pyramid Head after he accepted the darkness of the town after losing Mary, the last thing keeping him anchored to the real world.
- The Siam is the fourth monster in the series to resemble a form of "fusion" between two people. The others are the Abstract Daddy, the Two-Back, and monsters from Sinner's Reward that are seen surrounding Sara Linwood. Although highly suggestive, the Siam is the only monster where the two figures do not appear to be engaged in a sexual position with each other.
- The Siam's namesake could be an allusion to "siamese twin", a dated sobriquet for two people born physically conjoined to one-another.