Doom

Lucifer the Doom is a melee strength Hero with strong farming capabilities, good versatility, and one of the strongest single-target spells in the game. His very low starting armor makes him vulnerable to harassment, but his abilities and high health allow him to lane or even jungle quite effectively. A ruthless demon, he possesses malicious abilities revolving around greed, fire, and death. His Devour ability allows him to consume creeps, providing additional gold and allowing him to absorb any powers that creep had, which potentially allows him to have up to six total hero skills. Because there are numerous neutral creep abilities to choose from to supplement his other skills, the role that he chooses to play is quite flexible. Scorched Earth serves numerous purposes, allowing him to chase, escape, regenerate, and slowly burn his enemies all at once. LVL? Death is a spammable nuke that does either modest or massive damage to the enemy, depending on the enemy's level. Finally, his namesake ult Doom serves as one of the strongest single target lockdown abilities in the game. A unit afflicted with Doom takes intense damage over a lengthy duration, while having all his active abilities - even those from items - completely silenced. With numerous expensive items in his arsenal and a key enemy hero rendered useless for a teamfight, a farmed Doom ensures that nobody can extinguish his flame.

Tips

 * Doom has very poor Agility gain and one of the lowest starting armor in the game so it is essential to tank him up with armor items such as Assault Cuirass and Shiva's Guard to make his high HP go farther against physical attacks.
 * Be aware of heroes that commonly build Linken's Sphere as casting Doom on them will result in it being completely wasted. Cast LVL? Death on them first to burn the Linken's Sphere cooldown before casting Doom.
 * Cast Doom early in teamfights - the huge 15 second duration can render spell-dependent nukers such as Zeus or Lina virtually useless. Alternatively, if you can catch a hero carrying key support items like Mekansm and Pipe of Insight you can prevent those items from being used during the subsequent fight.
 * Make use of Devour's ability steal to give yourself and your team useful neutral creep abilities like Centaur Conqueror's stun, Hellbear Smasher's slow or Dark Troll Summoner's ensnare, or different types of auras.
 * Dark Troll Summoner is on the best creeps to devour for a jungling Doom. It gives Raise Dead, allowing you to summon two skeleton warriors who can tank other neutral creeps with only 50 mana. The other ability, Ensnare, helps you setup ganks or interrupt channeling enemies, but it has high mana cost so use it wisely.
 * The Wildwing Ripper's Tornado can also be used for jungling.
 * Another useful creep for jungling is Satyr Tormenter, its Unholy Aura provides great health regeneration (4 health/second), and can also be used while laning to help you and allies to hold lane longer. The Shockwave nuke is rather weak (125 magical damage) and high mana cost, but has good range and moderate cooldown, which you can use to finish off fleeing enemies with low health.
 * Hill Troll Priest's heal and mana regeneration aura are good for laning as well. The low mana cost healing spell can be useful against heroes who deal damage over time like Venomancer, Viper, Axe etc.
 * In lategame, one of the best options is an Alpha Wolf with passive critical hit chance (20 % for 2x damage) and 30% bonus damage aura.
 * A Satyr Trickster gives you a Purge spell on a very low (5 seconds) cooldown, it is a very versatile skill and is another strong choice. Remeber that it has very short cast range of 200, only a little over melee range.
 * A Kobold Foreman's movement speed aura can also be useful for pushing, ganking, chasing and fleeing.

Trivia

 * Several of Doom's abilities are inspired by Final Fantasy's Blue Mages. LVL? Death was probably based off of the Level 5 Death skill. Devour is highly similar to Quina Quen's eat and cook abilities from Final Fantasy IX. His ultimate, Doom, also shares the same name of another Blue Mage ability,  but the mechanics differ.
 * His name, Lucifer, is the name of a fallen angel who is known as the Devil in the Bible.
 * Despite his ultimate being a regular pentacle, a pentagram or pentacle is actually a symbol of protection, and does not mean evil or anything of the like, despite its current connotations. Paganism has no devil or Satan-esque figure. The picture/ability, to hold any sort of "evil", should be inverted, and due to the fact it changes direction when used on an enemy, should probably hold the face of Baphomet, too.
 * Doom's response "See no evil." upon picking up an invisibility rune refers to the Three Monkeys and their associated phrase: "See no evil, hear no evil, speak no evil."