Start out farming for health globes, any situation you can get one, go for it. Once you hit 13 you can definitely solo most mercs, but before that just stack up the regen for most of the time. Participate in teamfights to pick off the extra exp, but other than that don't engage enemy heroes too much. Focus on mercs and objectives a lot, and once you hit 16 you'll be able to shove drain hope on heroes pretty constantly, lowering the cooldown enough to use it 4 or 5 times in a teamfight. Once level 20 comes around, use your ult to heal yourself when you're below ~25% health, that way you get about 60% back from both the ult and the drain hope that activates. I find other builds die really easy at any point in the game, but this one ends up able to contend with Diablo and Butcher 1v1 at about halfway through the game.

Pick the entomb build if you have a lot of runners like Murky, Valla, Sylvanas, etc. Catch them after they use their traversal skills and boom, they're stuck taking 600 damage without moving along with your burning rage dps adding about 200, and the damage you can do with drain hope and skeletal swing. Use entomb to pick off stragglers more than catch and entire team. If everyone is low health and you have a good aoe fighter like Jaina, Raynor, Rexxar, Sonya, etc., then that would be a perfect time to use it on an entire team, other than that it's risky.

This build is great for maps with objectives you have to kill and gather, along with Battlefield of Eternity, but Dragon Shire and Cursed Hollow are a little bit of a trick to get down since you can only take the mercs so often and standing around is dangerous for Leoric due to his slow speed.

Try it out and have fun. You'll be op on blackhearts bay, able to take dubloon camps solo at about level 7 or 9.

So Tomb is a lot more worthy than I thought. I made it out to be pretty worthless, assuming other guides were right, and it's really formidable for either escape or taking the money.