We start off with Mystic Tomato:
When this card is destroyed by battle and sent to the Graveyard, you can Special Summon 1 DARK monster with 1500 or less ATK from your Deck in face-up Attack Position.
Tomato is your average recruiter monster, which we have mentioned many times. It has an Optional Trigger Effect that you activate at the End of the Damage Step. It doesn't target. It cannot Special Summon monsters with "?" ATK.
Next, we have Viser Des:
When this card is Normal Summoned, select 1 monster your opponent controls. Destroy that monster during your 3rd Standby Phase after the Summon. This card cannot be destroyed by battle until this effect is resolved.
Viser Des's first effect is Mandatory Trigger Effect activated upon its Normal Summon, meaning you can use Pulling the Rug against it. This effect targets. This effect will also destroy the target monster a few turns later, but since it won't do so when it resolves, effects like Stardust Dragon cannot negate this effect. The destruction also doesn't use the chain either. Furthermore, until these turns pass, Viser Des cannot be destroyed in battle. If either Viser Des or the target are Removed from the Field, the target won't be destroyed and Viser Des is no longer protected from being destroyed in battle. If Viser Des is flipped face-down, the target won't be destroyed either. If Skill Drain is activated and is later destroyed, then Viser Des will keep targeting the monster, so once Skill Drain is gone, it will still be protected from battle and will still destroy the monster at the third Standby Phase.
Moving on, we have Legendary Fiend:
During each of your Standby Phases, this card gains 700 ATK.
Legendary Fiend has a Mandatory Trigger Effect. If Fiend is flipped face-down, Removed from the Field, or has its effects negated, it will lose all the ATK gained through the turns.
Then, we have Dark Jeroid:
When this card is Normal Summoned, Flip Summoned, or Special Summoned successfully, select 1 face-up monster on the field. As long as the monster remains face-up on the field, decrease its ATK by 800 points.
Dark Jeroid has a Mandatory Trigger Effect activated upon its Summon (so it can be negated by Pulling the Rug or Swallow Flip accordingly). This effect targets, and if Dark Jeroid is Summoned while no other monster is face-up, it must reduce its own ATK. The ATK reduction does not depend on Jeroid's existence on the Field.
We also have Newdoria:
When this card is destroyed by battle and sent to the Graveyard, destroy 1 monster on the field.
Newdoria has a Mandatory Trigger Effect that you activate at the End of the Damage Step. It targets a monster.
Then have Drillago:
When there are only face-up monsters with ATK 1600 or more on your opponent's side of the field, this monster can attack your opponent's Life Points directly.
Drillago has a Continuous Effect that allows it to attack directly. The only Cards that your opponent must control are face-up monsters with high enough ATK.
Moving on, we have Bowganian:
During each of your Standby Phases, inflict 600 points of damage to your opponent's Life Points.
Bowganian has a Mandatory Trigger Effect. Not much else to say.
And finally, we arrive to the most emblematic monster used by Marik, other than the illegal The Winged Dragon of Ra: Lava Golem:
This card cannot be Normal Summoned or Set. This card can only be Special Summoned to your opponent's side of the field by Tributing 2 monsters they control. You cannot Normal Summon or Set the turn you Special Summon this card. The controller of this card takes 1000 points of damage during each of his/her Standby Phases.
Lava Golem is Special Summoned through an Inherent Special Summon. It's Summoning Condition is one of the few times in this game in which you can use your opponent's Cards to pay your own tributes. Lava Golem is considered to be Summoned by the player that holds it in his/her Hand, and it's Summoned to the opposite player's side of the Field. This means that the opposite player can activate Bottomless Trap Hole, even though the monster is on his/her own side of the Field, because it was the other player who Summoned Lava Golem. Other than that, its effect to inflict damage is a Mandatory Trigger Effect.
That's all for this first part of the review of Marik's Structure Deck. Stay tuned for some Gravekeepers!