Leoric is a Warrior class that can dish out some pretty decent damage if your party needs a boost. Like many of the other Warrior class heroes, he has plenty of ways to stay alive, but his Undying passive trait allows him to remain on the battlefield, unlike most other heroes. If you're looking for a solid tank for your party, but you always want the option to dish out some damage, Leoric is a good choice.
Leoric's Skeletal Swing attacks all enemies in a wide arc directly in front of him. This is going to be your most used attack as Leoric and can easily clear waves of minions when you're soaking lanes. It also slows heroes by 40 percent for 2.5 seconds after you connect with it, which works very well if an opposing hero is trying to escape your grasp. Use this often, but have it ready to slow an opponent if you feel they'll try to run.
Drain Hope is an attack that can only be used against opposing heroes and must be used skillfully. This is Leoric's primary self-heal, but it's easy to avoid if you're not using it correctly. Leoric grabs the target's soul, draining up to 25 percent of their maximum health and giving it to Leoric over the course of four seconds. However, while the ability is active, Leoric is slowed by 20 percent. If you use it on an opponent that's too far away from Leoric, the opposing hero will be able to run out of its range pretty easily, effectively wasting the technique. Use it at close range, and preferably against heroes that don't have quick escape options. It has a 12 second cooldown, so use it wisely or you'll be without self-healing for most of a team fight.
Wraith Walk is Leoric's primary escape option. He separates his soul from his body and becomes unstoppable for 2.5 seconds while gaining a 50 percent movement speed boost. Once the ability comes to an end, Leoric's body jumps to the location of his soul. Use this when you're in trouble and need a way to get out quickly. Think of it like Leoric's version of Blink except that it also cancels many Heroic abilities such as Nova's Triple Tap.
Leoric's passive trait allows him to always remain on the battlefield and never die. When he loses all of his health he becomes a ghost and can still wander around the battlefield. He won't be able to inflict any damage, but he still has a health bar that slowly fills. Any attacks or abilities that heal will still heal Leoric, speeding up his return. When he reaches full health he comes back from the ghost state in whatever location you moved the ghost to. You can use this to scout enemy movements after you've "died" or to simply put yourself in a good position to attack or defend as soon as your health regenerates.
Tanking and Damage Build
Level 1 - Reanimation or Hopelessness
Level 4 - Willing Vessel or Fealty Unto Death
Level 7 - Ossein Renewal
Level 10 - March of the Black King or Entomb
Level 13 - Crushing Hope or Drain Momentum
Level 16 - Consume Vitality or Renewed Swing
Level 20 - Death March or Buried Alive
Your primary choice at level one should be Reanimation. For every Regeneration Globe you gather, Leoric's health regeneration rate will increase, even while he's in ghost form during Undying. It also gives you the ability to pick up Regeneration Globes during Undying. All of this equates to Leoric coming back from the ghost state much faster the more your collect Regeneration Globes. If you happen to be going against a Valla or some other Assassin who does damage with basic attacks, you can pick up Block to help soften the blow, but if you're not going with Reanimation your only practical choice should be Hopelessness, which increases the range of Drain Hope to make it harder to escape from.
When you reach level four you should generally take Willing Vessel to increase the healing your receive from Drain Hope from 25 percent of your maximum health, to 30 percent. If you're just starting to play as Leoric and you aren't landing Drain Hope as often as you should be, you can opt for Fealty Unto Death. This replenishes health and mana anytime a minion dies in close proximity. However, keep in mind there will be plenty of fights that are not close to minions, making this ability useless in some situations.
At level seven your first choice should be Ossein Renewal, which is Leoric's second self-heal. This one has a 60 second cooldown, but replenishes 20 percent of your maximum health over the course of 6 seconds. This works best during the Undying state to get you back in the fight faster, but can also save your life if you're getting low and Drain Hope is unavailable. Ghastly Reach can also be useful in limited situations as it increases the range of Skeletal Swing by 25 percent, but it's very situation and is primarily effective against long-range heroes such as Sgt. Hammer.
Leoric's level 10 selection should be March of the Black King if you're going for a damage build, or Entomb if you need more crowd control options for your team. March of the Black King deals a decent amount of damage and heals Leoric at the same time. Entomb creates a tomb directly in front of Leoric that stops anyone trapped inside from getting away. You can use this to essentially trap opposing heroes while the rest of your team finishes them off.
When you reach level 13 you have a choice between Crushing Hope and Drain Momentum. Crushing Hope will inflict additional damage if Drain Hope hits an enemy for the entire duration of the ability. Go with this choice if you're good at landing Drain Hope or you're going for a damage build. Drain Momentum removes the decreased movement speed that occurs when using Drain Hope so you can land it easier.
At level 16 Consume Vitality should be your first choice. When you use Skeletal Swing, it heals Leoric for up to 10 percent of his maximum health depending on how many enemies are hit by the attack. This works very well once you're in the Undying state so you can return to the land of the living much faster. Renewed Swing allows Leoric to use Skeletal Swing a second time for no cost within three seconds of using it the first time. The damage is cut to 50 percent, but if you're going for a damage build, this should be your selection.
Finally, level 20 brings Death March or Buried Alive depending on which Heroic you selected at level 10. Death March allows the final hit of March of the Block King to inflict Drain Hope on all enemies in close proximity. Meanwhile, Buried Alive causes enemies encased in Entomb to take damage over time.