Ok, for reference here are the most common Codex cards that deal with +1/+1 counters:
Moss Sentinels: Forest’s Favor, Blooming Ancient, Blooming Elm
Flagstone Dominion: Boot Camp, Drill Sergeant
Whitestar Order: Sparring Partner
Bloom and Forest’s Favor are functionally the same card and they both carry the condition ‘that doesn’t already have a +1/+1 rune’. Both of these cards can put +1/+1 counters on units and/or heroes and generally speaking +1/+1 counters are much stronger on Heroes since you can heal them potentially twice without much effort. These spells are in Starter decks and therefore you will see them fairly often, but I would consider them to be an average starter spell.
Sparring Partner is a Tech I unit that can affect heroes or units, but it also carries the conditional ‘that doesn’t have a +1/+1 rune’. It’s quite good despite this restriction because it encourages you to spread runes around and not pile them onto one unit/hero. The ability to do it more than once per turn is also quite strong and I’ve seen it played quite a bit as well as used it myself often.
Blooming Ancient and Drill Sergeant are functionally very similar, but Blooming Ancient is a bit stronger. Blooming Ancient triggers when ‘a unit or hero arrives’ while Drill Sergeant triggers when ‘you play a unit from your hand’. They both have the exact same ability to ‘remove a +1/+1 rune -> put a +1/+1 rune on another unit’. Both cards cannot give runes to heroes, but Blooming Ancient is easier to trigger. Both are also Tech II units, so these engines are designed to end games or at least set up very strong boards.
Blooming Elm is unusual for several reasons. First it is a building rather than a one-shot spell or an engine creature, second despite being a Tech II card it carries the conditional ‘if that unit or hero doesn’t have any +1/+1 runes’. This is inconsistent with the other 2 cards that are similarly difficult to get online Tech II cards. It also makes this card rather weak (I’ve never read about it being played in a match or played with it or against it). It has some synergy with Blooming Ancient (since you can move runes off of Ancient, then re-up 3 more runes), but this restriction hamstrings it from being truly powerful.
Finally we have the best for last - Boot Camp. Boot Camp is a really OP spell that you see all the time. There are several reasons for this, but lets look at it compared to other effects of this type:
- It’s easier/faster to get online than the Tech II options
- It’s cheaper than the starter spell options
- It can be used multiple times on the same unit/hero, unlike all other non-Tech II options
- It cantrips (You draw a card after playing it)! That’s really awesome especially on an already-cheaper-than-it-should-be card.
- It can be used offensively as a mini-Arrest, though this is obviously a tempo play
Now Boot Camp is not all upside. Since it exhausts the unit/hero it targets, you can’t give a unit or hero a +1/+1 rune and then attack with it. You can attack then use it on an exhausted unit/hero (which seems like a flavor fail). Oni also can’t use it on himself. Boot Camp is inconsistent with how the rest of the game handles +1/+1 runes for non-Tech II engines. I don’t think it’s an accident that the purple starter gets paired with the Peace spec for precisely this interaction which works well on Hardened Mox.
Ideally Boot Camp should require a non-exhausted hero or unit and would be restricted to units/heroes that don’t already have a +1/+1 rune. This would make it more consistent with the rest of the game and help balance some of its incredible utility with being more conditional. Blooming Elm should lose its restriction to target units/heroes without +1/+1 runes because it is a weak card in a very strong spec and it may become a more viable card.
Edit: I removed the Nullcraft aside.
Edit2: Changed Title from ‘Balance’ to ‘Design’