I am now playing this game, and am using the DLC (my Vangal may be my most powerful character at this point). One of my favorite things to do with these sorts of games is to experiment, and see how things work. In any case, I am going to post some of my observations here:

Rapturous Chant: Restores 1.8x MND to all allies. (The description doesn't mention the amount restored.) It does kill the user, but that isn't always a bad thing; in conjunction with revive effects, this can be used to move a character across the map faster, plus the only non-item guaranteed full heal is Revive II. I would say this is my favorite ability so far. (I actually used this in conjunction with Revive I to quickly clear a mission where I had to reach a specific spot.)

Healing Staff: This weapon is one I've been wanting to play with a bit, and here are some observations:
* Some counters, like counterattack, will not trigger when attacking with this weapon. It seems that counters that only trigger from offensive actions won't trigger with this weapon.
* Abilities that "count as a regular attack" will do damage; the healing effects will not occur.
* I haven't actually tried it with Infused Edge yet, but that attack "does a regular attack" so it might end up healing the target; if it does, this means it won't work well the way Infused Edge would normally, but keep in mind that Infused Edge works with beneficial spells.

Edit: One other thing: I don't know whether the AI knows how to use the Healing Staff effectively, but I did see an enemy with the Sylvan variant attack another enemy to heal it. Note that attacks with this variant are affected by facing, and I think the Healing Staff is as well, so attacking from behind yields more healing.

And I found a bug. (No, I'm not talking about a Bzil here.)

Infused Edge + Healing Staff will, in fact, heal the character with the regular attack. However, there is a bug with the displayed healing prediction.

If you infuse a healing spell, the predicted healing will be that of the attack minus the healing of the spell, while the actual healing will be the sum here.

If you infuse an attack spell, the predicted healing will be that of the attack plus the damage the spell would do, but the actual result is that the attack spell still does damage, so you could actually end up doing net damage even if healing is predicted.

This may be just a cosmetic bug, but I am wondering if the AI fails to use this particular combination properly. (Can enemies spawn with Healing Staves equipped?)

One more thing, for anyone who happens to find this thread:

* Unlike Rapturous Chant, a death from Final Chant *will* result in an injury.

(Also, it seems Rapturous Chant doesn't cure everything; it doesn't seem to cure Root, for example.)

Some skill interactions with the DLC:
* Vicious Criticals + healing abilities: The healing spell will critical, but will not inflect Poison and Bleed. (So giving this to a Niwot or a character with Healing Touch is a reasonable setup.)
* Focus Fire + Mass Heal I: The result is a single target heal that heals more than Mass Heal I. (In other words, it works in a useful manner, and one you would expect.) (This may be possible without the DLC, by using a certain ability that copies the primary ability of another battle participant.)
* Healing Touch + Sap Power: Your regular attack will heal allies, but will also dispel beneficial effects. (Not sure whether or not the target has Renew afterwords, as it both applies and removes the effect.) (This is an example of what I call an anti-combo, and it is not a good idea to combine these.)

For purposes of Wrangler skills, Bzaro does not count as a monster. For example, his death won't trigger the Owner's Pride boost.

Also, I believe monsters that you tame do not drop essences.

Razor Wind (from Samurai, requires DLC):
* Can't be used with non-offensive abilities like Field Aid (rather disappointing here)
* Can't be used with Infused Edge
* Can be used with other skills that have Weapon range

Double Cast's spells are at 75% power; this includes Revive II, which will only restore 75% of the target's HP.

Now I just need to see if there's a way to increase its power, then check the interaction with Arcane Engine.

Healing Staff:
* Does not heal when using "counts as regular attack" abilities
* Will trigger Blessed One
* With Leech Mana, the attacker will gain MP based off the amount healed (this is contrary to Final Fantasy 7's handling of a similar situation)

Blood Staff:
* Drain effect works when using "counts as regular attack" abilities
* Can still trigger Leech Mana to get MP back (wondering if Leech Life will give you over 100% of the damage as HP)

Also:
* Legendary Healer does not appear to affect Revive II.
* (Does Legendary Healer affect the Healing Staff?)

Here's one that's really just cosmetic, but is an interesting touch:

A Drake Zotzit with Breath Attack will fire multiple needles, one at each target, when attacking.

One more:
* If a character has both Double Cast and Double Cast 2 equipped, only Double Cast 2 can be used. (Yes, Double Cast 1, if it were usable, would have a use in this situation; sometimes you need to do control damage. For example, you might not want to end a battle just yet, you may want to use Collect Pelt/Bounty/Trophy on the enemy, or (if you have the DLC) you might want to tame the creature.)

Here's another one I found out.

Anyone wonder what happens if you combine Tag Team (swap an active monster for one in your reserves) with the Tyrant's Band?

It turns out that the game won't let you use Tag Team at all if you try this.

A few more, mainly related to Quicken and Rebirth:
* If Quicken is cast twice in one turn, the second target is the one that gets to act first.
* When Rebirth triggers, it does not interrupt the turn. This means that, if the first action of Double Cast results in the caster dying and Rebirth triggering, the caster can still cast a second spell. (This matters if the DLC is in use, as it makes it possible to use Double Cast with spells like Final Chant or Kamikaze, though it's possible with the Spymaster's final skill without it.)
* When Rebirth triggers, all (temporary) status effects are removed. This means that a character who was just Quickened (and hence Exhausted) can kill themself with the first spell, come back to life via Rebirth, and then cast Quicken on themself and it will work.

This is true of speed ties generally, the last person added goes first. This can also be used to control turn order at deployment (by placing the one you want to go first on the map last)

Coalesce (from Pektite):
* Will grant the revived character all buffs the caster has, even those from equipment or auto-abilities.
* Rebirth will *not* trigger when Coalesce is used. However, in this case, the revived character will have Rebirth status.
* If the caster has Auto-Rebirth or is wearing a Phoenix Band, and the spell is cast before Rebirth has been activated, the Rebirth status will persist through death; if the original caster is later revived, they will still be in Rebirth status. (This is contrary to usual behavior, where death removes all status effects, including Exhausted as I mentioned earlier.)
* Coalesce will trigger Turnabout on the caster. This is usually not a good thing, as the newly revived character is guaranteed to be hit by it.

By the way, different elemental pektites have different stats; thunder gives more speed, while earth gives less speed but even more defense (in case you thought that defense growth of 11 isn't enough).

Item Potency (and another bug):
* The Full Potion's effect is doubled; this is only likely to matter if it's paired with Arcane Engine, allowing 198 MP to be restored at once. (Just add Focused Rage or Zohl Beam for massive damage!)
* (BUG) If the DLC is installed, recruited Kawa get an ability called Item Potency, which claims to double the effect of items, but it does not actually have that effect. (It does at least allow the Kawa to use items, however.)

Focused Rage and Zohl Beam seem to be about the same strength (assuming ATK and MND about the same), but Focused Rage can get a bonus for a back attack. Zohl Heal is stronger (probably due to ignoring defense); this can trigger Arcane Engine, though I do not know whether over 100% efficiency (which would allow exponential MP gain) is possible.