To the best of my knowledge, there have been two cards with an effect similar to Conclave Mentor, and both of them saw substantial amounts of play — Hardened Scales and Winding Constrictor.
Of the two, Conclave Mentor is much closer to Winding Constrictor than to Hardened Scales. Given that Winding Constrictor was a very important player during its time in Standard and that wasn’t even that long ago, it makes sense that Conclave Mentor could be as well.
On the surface, it seems like Winding Constrictor was a better card than Conclave Mentor will be. It had an extra point of toughness, which is obviously very relevant in a world where people can play Shock and Bonecrusher Giant (as well as for blocking), and it worked on any types of counters, not just +1/+1 counters (one of the big uses of the card when it was in Kaladesh Standard was to improve your energy gains). Winding Constrictor was very strong, though, and being a slightly weaker card should not disqualify Conclave Mentor from Standard play. Furthermore, I’m not actually convinced Conclave Mentor is weaker and it could actually end up being the better card.
In return for its shortcomings, Conclave Mentor has a lifegain trigger. It won’t be relevant a lot of the time, but the same could be said for Winding Constrictor’s benefits — sometimes the third toughness wasn’t relevant and some decks played it with only +1/+1 counters to double. There will be games in which gaining that two life will be the difference between winning and losing and you can often gain more than that, as you’re obviously incentivized to pump your creatures in a Conclave Mentor deck.
If this was the only thing, Winding Constrictor would clearly be superior — one point of toughness is just worth more than the two life you get if Conclave Mentor dies. However, it’s not the only thing; Conclave Mentor’s biggest strength is in its colors. Winding Constrictor was basically a green card in a Golgari body. All the +1/+1 counters you were ever doubling came from green cards, as there’s just not that much support for the mechanic in black. White, on the other hand, has a lot of support for it, and there are many white or Selesnya cards that would benefit from this effect.
So, where would we play Conclave Mentor? Clearly it has to be an aggressively-slanted deck. After all, you need a lot of creatures and ways to pump them. Repeatable ways of adding counters (or cards that add counters to many different creatures) are better than cards that add a lot of counters at once, since those only get increased by one. Here’s a non-comprehensive list of cards I’m interested in trying out with Conclave Mentor:
- Cards that put repeated +1/+1 counters on themselves or others
- Cards that put +1/+1 counters on a lot of creatures at once
- Cards that add counters once
One-time effects aren’t very exciting with Conclave Mentor (you’re only getting +1/+1 in the end), but many of these creatures are good cards to add counters to, and they work with proliferate very well, so they might have a spot. Stonecoil Serpent in particular is just a good card regardless of Conclave Mentor, so it will show up in a lot of these lists.
I think that there are many possible directions with Conclave Mentor – white-based, green-based, artifacts, and something in between. Let’s examine them.
White-Based Conclave Mentor
White-based Conclave Mentor decks will be similar to Mono-White Aggro, but with a focus on +1/+1 counters — they will try to go wild. These decks probably cannot afford to play something like Pelt Collector, as the Turn 1 green is prohibitive and they wouldn’t have many big creatures to pump it anyway. Basri Ket seems like it could be sort of a glue that holds things together here, as it is both a pump effect that gets boosted by Conclave Mentor and a card that rewards you for going wide and generates more bodies for you to pump. Venerated Loxodon, of course, is a very good card here as well.
Creatures (28)
- 4 Venerated Loxodon
- 2 Hunted Witness
- 4 Giant Killer
- 4 Stonecoil Serpent
- 4 Seasoned Hallowblade
- 2 Basri's Lieutenant
- 4 Selfless Savior
- 4 Conclave Mentor
Planeswalkers (5)
Lands (22)
Spells (5)
This is very similar to a regular Mono-White, except it’s splashing green for Conclave Mentor and Ajani, the Greathearted. Is it worth the troubles with the mana and losing Castle Ardenvale? Maybe, possibly not, but we won’t know it until we try it. You really want to cast a one-drop on Turn 1, so Temples are a bit weird, but Forest won’t cast most of your one-drops anyway and you can always play Temple on Turns 2 or 3 (alongside more one-drops). To make the mana better, you could cut some of the white one-drops for Chamber Sentries, but I don’t think that card is good enough without proliferate.
As an aside, I’ve seen many Conclave Mentor decks playing The Ozolith, but I just don’t think that’s very good. The metagame right now doesn’t have a lot of spot removal and between Hunted Witness, Selfless Savior, Seasoned Hallowblade, Unbreakable Formation, and Basri’s Lieutenant, you seem very well protected against sweepers already. It’s possible that, if the metagame changes a bit, The Ozolith becomes a good card, but right now I wouldn’t start it.
Lifegain Conclave Mentor
Here, the goal is to use Conclave Mentor to power up Ajani’s Pridemate and Heliod, Sun-Crowned. It will still play like a Mono-White Aggro deck, but will have that lifegain angle.
Creatures (33)
- 4 Ajani's Pridemate
- 4 Healer's Hawk
- 4 Venerated Loxodon
- 2 Linden, the Steadfast Queen
- 3 Daxos, Blessed by the Sun
- 4 Heliod, Sun-Crowned
- 4 Alseid of Life's Bounty
- 4 Conclave Mentor
- 4 Speaker of the Heavens
Planeswalkers (2)
Lands (23)
Spells (2)
I think this deck has steeper white mana requirements, since it plays Daxos, Blessed by the Sun and Linden, the Steadfast Queen, but at the same time it’s less reliant on just getting on the battlefield early, so you can afford some more taplands.
Blossoming Sands is an experiment. Obviously having another tapped land is bad, but the lifegain from it could actually translate into two or four +1/+1 counters in some situations, so it could definitely be worth it.
Green-Based Conclave Mentor
Green-based versions of the deck will be slightly different. They will not try to go wide as much, and instead will have fewer threats that will grow significantly bigger. They will play, not surprisingly, much more like Mono-Green decks than Mono-White decks, and they will be more vulnerable to spot removal than to something like a Flame Sweep.
Creatures (32)
- 2 Scavenging Ooze
- 4 Pelt Collector
- 4 Growth-Chamber Guardian
- 3 Huatli's Raptor
- 4 Questing Beast
- 2 Wildborn Preserver
- 4 Stonecoil Serpent
- 2 Yorvo, Lord of Garenbrig
- 3 Gemrazer
- 4 Conclave Mentor
Planeswalkers (3)
Lands (25)
I think this deck has enough +1/+1 counters action going on that it can actually use Huatli’s Raptor (which is also a pretty good follow-up to Pelt Collector). However, it’s not so clear to me that Evolution Sage isn’t better — it works very well with Fabled Passage and you can even play Evolving Wilds if you want to. If you have a Conclave Mentor on the battlefield, going Evolution Sage + Fabled Passage will give all your creatures with counters a permanent +4/+4, which is obviously very strong.
Another possible direction for a green base is playing a little more white to include Venerated Loxodon. Venerated Loxodon is traditionally better with cheaper, smaller creatures (after all, you don’t want to be tapping your 6/6 to add a counter to it – you want to be attacking with it), but it’s such a good card with Conclave Mentor that it might be worth trying to make it work in a green-based build.
Creatures (33)
- 4 Venerated Loxodon
- 4 Pelt Collector
- 3 Chamber Sentry
- 4 Growth-Chamber Guardian
- 4 Huatli's Raptor
- 4 Stonecoil Serpent
- 4 Gemrazer
- 2 Basri's Lieutenant
- 4 Conclave Mentor
Planeswalkers (2)
Lands (25)
Since we’re adding Venerated Loxodon, I think that’s enough to justify Chamber Sentry (which can be played as a one-drop for fast Loxodon draws), which also makes Huatli’s Raptor better and works quite well with Gemrazer.
Artifact-Based Conclave Mentor
Having an artifact-based deck allows us to play two of the best cards with Conclave Mentor — Steel Overseer and Karn’s Bastion. Karn’s Bastion has never had a lot of traction but in the right deck it can act as a Gavony Township, and if you have one (or multiple!) Conclave Mentors out, then it becomes really strong. I feel like the mana requirements of the white and green versions don’t allow you to play it, but an artifact-based build easily could.
Creatures (30)
- 4 Steel Overseer
- 4 Venerated Loxodon
- 4 Chamber Sentry
- 4 Huatli's Raptor
- 4 Gingerbrute
- 4 Stonecoil Serpent
- 2 Lurrus of the Dream-Den
- 4 Conclave Mentor
Planeswalkers (3)
Lands (24)
Spells (3)
There are a lot of small synergies in this deck, such as Basri Ket with proliferate and Steel Overseer with Unbreakable Formation (which gives it vigilance, meaning you can attack with it and tap it in the same turn).
Lastly, there might be a potential Adventures build somewhere. This deck won’t do as good a job of adding counters to its creatures, so Conclave Mentor will not be as good there, but it draws a reasonable amount of extra cards and puts a lot of bodies on the battlefield, so whenever you do add counters to everything you’ll be adding a ton of counters.
Creatures (24)
- 4 Venerated Loxodon
- 4 Lovestruck Beast
- 4 Faerie Guidemother
- 4 Giant Killer
- 4 Edgewall Innkeeper
- 4 Conclave Mentor
Planeswalkers (3)
Lands (23)
Spells (10)
Overall, the biggest thing that seems to be holding Conclave Mentor back is the mana. I think the support cards are there, but it’s hard to make them work together since the mana requirements are so intense. If someone finds a way to make the mana work well, Conclave Mentor decks have the potential to become the new wave of nonred aggro in Core Set 2021 Standard.