Have you thought of subbing in Serene Steward for the Ondu's?

C7M8, I have indeed thought of that, and even tried that. Ultimately, I decided to not include it, though. It's a great card, but I needed to draw the line somewhere so that I don't end up with too many creatures. Too often I didn't actually have the 1 mana available to generate the counter, so I just had a 2/2 creature whose ability I rarely used. I decided to instead go with Vampire Envoy because I get a 1/4 flier that gains me life when it gets tapped.

I know that the biggest weakness of this deck is that creatures are low toughness and power, but if 3 or 4 can get out at the same time then each becomes a bit harder to deal with because of all of the abilities that can get triggered by affecting 1. Ultimately, I decided that Serene Steward just didn't work well for me. Again, it's a good card, just not working well for me at my local FNMs.

With Ondu War Cleric, if I held it back to do defense, I can do the ability at the end of the opponent's turn (it's an ability that can be activated at instant speed, so it doesn't have to be during my turn) and untap it at the start of my turn. If I leave Vampire Envoy also untapped, then I get 3 life. Most importantly, I didn't have to pay any mana for this.

Thanks for the suggestion, though! I have tried it and just decided that for me and for the location I play that it just didn't work quite as well. Against decks in other stores it may be fine-- different flavors in each area.

Sorin, Grim Nemesis damages the opponent plus draws a card with his first ability and has life gain / creature removal with his second. Anguished Unmaking for great removal since you can spare the life.

As a side note, Gideon, Ally of Zendikar's first ability does not trigger Kalastria Healer, since he was already on the battlefield and rally is an ETB effect. His second ability still does though.

Fal1enKing, yes, thank you for catching my mistake with Gideon! Not sure why I put that in there because I know that you are correct. Must have been in a hurry and wrote that without thinking. Changing it when I finish this response.

I have deeply considered Sorin, Grim Nemesis and he would fit nicely in many ways. I agree that he is a good fit!

Anguished Unmaking, I have mixed feelings. You say that I have life to spare, but that's not often the case. It's a great card and it's at instant speed, but I prefer paying 1 extra mana for Quarantine Field. I can also side in Stasis Snare if it's creatures that need to be targeted at instant speed.

Thanks for the suggestions!

Problem with those white removal is that people will side in removal against them. Still, if it works where you play this deck, that's what matters.

Quarantine Field is still an enchantment and is vulnerable to Felidar Cub and Dromoka's Command while Anguished Unmaking is an instant speed removal that can affect plainswalkers. Declaration in Stone is handy as well if they are using thopters or dropping lots of cheap value cards such as Sylvan Advocate.

Lordeh and Fal1enKing, Quarantine Field will work against any non-land permanent, so it, too, will work against planeswalkers. Granted, it is not instant speed. True, as an enchantment, it is subject to removal, but, in my experience, that's exceptionally rare (this last Friday was the first time I ever had that happen, in fact). I think Quarantine Field is used infrequently, so there aren't as many people expecting it.

Unfortunately, Stasis Snare and Silkwrap have become quite popular in the last couple of months. The person who snapped my Quarantine Field (different deck, but same card) said he specifically sidebaorded it because of those two cards.

I get why people like Anguished Unmaking, I just have a hard time with the 3 lost life. However, when facing Ormendahl, Profane Prince  ^Flip or Ulamog, the Ceaseless Hunger, 3 life doesn't looks so terrible to lose, does it?