Recommendations for a friends Meren deck.

Bloodsoaked Altar: Although it costs a bit of mana, this card can be extremely powerful. Sacrifice a creature you don't need, discard a creature card that you can get back with Meren, and pay 2 life for a 5/5 demon. If not removed in a few turns, Bloodsoaked altar and its demons can quickly win you the game.

Bolas's Citadel: This card simply makes sure you always have fuel, even if it costs some mana. No turn will go by with "Draw a card; Play a land. Go to end step, return something with meren, then pass". Although it costs some life, it provides some nice benefits and, if you can build up a board state, it can also win the game.

Boneyard Mycodrax: This card is great late game when you have a ton of stuff in your graveyard. you can either bring it out for a simple offensive/defensive creature that keeps recurring, or if you have a flying or trample creature, you can put a ton of +1/+1 counters on a creature to win the game.

Burnished Hart: Constant recurring land fetch. enough said.

Embodiment of Agonies: Requiring only three experience counters to return to the battlefield with meren, embodiment of agonies can be a constant big flying, deathtouch threat. He can win games, and can keep big attackers at bay.

Garruk, Cursed Huntsman: Garruk creates a lot of 2/2 wolves, which benefit from chump blocking or randomly attacking your opponent. Combined with other death triggers, these wolves can be very beneficial. If you need to kill something, his -3 can be a big help while drawing you a card. Lastly, his emblem buffs all of your creatures, helping you win the game.

Gravebreaker Lamia: I won't lie, this card can just search your library for Spore Frog. You can search for something else, but come on; Unless you already have spore frog, what else are you going to search for?

Kogla, the Titan Ape: Kogla provides three things to this deck; Removal with its fight ability, which can be triggered multiple times with meren. You can remove pesky artifacts and enchantments with his attack ability. And lastly, if an opponent tries killing meren or destroying all creatures, you can pay 2 mana to get it in your hand instead.Although 2 mana is the commander tax, this means if meren has been sent to the command zone twice in the game, you're saving 2 mana in total.

Moldervine Reclamation: Gain life and draw cards for creatures dying. Simple and very useful.

Putrefy: Remove a pesky creature or artifact.

Skull Prophet: This card provides mana, while also being able to put more cards into your graveyard. Which ever is necessary.

sr konrad, the grim: Konrad is a great wincon. His ability is pretty wordy and complex, but people will help you get it right. Did a creature die? Each opponent is dealt damage. Did you return a creature to your hand or the battlefield with meren? Each opponent is dealt damage. His second ability can fill your graveyard with creatures as well, which is pretty neat.

Thorn Mammoth: A good trample creature that also helps you kill small and medium creatures your opponents control. Since meren can return a creature from your graveyard each turn, you will always trigger thorn mammoths ability once. You can even suicide it into a 6/6 creature and return it with meren to kill another creature.

Thragtusk: Helps you not lose the game as quickly and, along with abilities that sacrifice creatures, creates 3/3 beasts for you.

Void Beckoner: Since meren can return cards to your hand, void beckoner allows you to draw a few cards if needed. In addition, it encourages players not to attack you since you're creatures will have deathtouch.