Our campaign will reach level 4 next session.

I was very excited to choose the new Battle Familiar from Arcana Unleashed for my wizard. The problem is: my DM is concerned about the balance impact of a concentrationless summon, especially if more than one player takes the spell. She fears that she'll have to add too many monsters to each encounter to compensate for it.

What do you think - is the spell really that much of a gamechanger? Is it necessary to rebalance encounters because of it?

In case you don't have access to the spell yet, the full text is visible in this video (right at the start):

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It will cause interpretation issue when casting it on your existing familiar regarding what features it retains since the wording is not clear enough

The text clearly says it "your familiar can attack in addition to taking other actions as normal, and your familiar’s game statistics are replaced by the Battle Familiar stat block, but it retains its creature type, alignment, Hit Points, Hit Point Dice, and any features granted by the Find Familiar spell."

so the problem relies around "any features granted by the find familiar spell" on what does that include.

It’s balanced 🤷‍♀️ if the GM wants the familiar to be dropped, enemies can focus on it and kill it

It's pretty strong in tier 1 of play, sure. Nothing new. Same for warlocks with chain invocations is tiers 1 and 2, but at tier 3+ is kinda bad.

If your DM rarely or never AOE your party, yes, it can be a problem.

Now casters can summon one more pet martial of their own. Without precasting, I don't think it is broken. But with precasting, it widens the caster-martial gap even further.

I believe the retained features are the "deliver touch spells" and "see through their eyes" effects that come from the spell, but nothing from the stat block (like speed or skill proficiencies).

At least that's how most people I've seen talking about the spell have interpreted it so far.

Yeah, that's how I read it, and why it gets a Just OK.

As a Chain lock, if I can stack just tHP on a Pseduodragon, Sprite or Quasit, I would be a menace.

For combat it's ok, the problem is the fact that it flies and you can mount it if you are small, so it becomes a better fly spell that doesn't require concentration and costs a second level slot instead of a third

It can deliver touch spells

If you have warlock invocations that apply to Find Familiar they continue to apply

It is open ended so I believe the other new familiar feats would still apply as they apply to Find Familiar and it says it retains anything granted by Find Familiar. That is how I would rule it anyway

I am itching to play new necromancer. Upcast animate dead with each skelly having + int necro damage that ignores resistances is crazy good. And if ony can make a skelly battle familiar - should be so good.

Purely by itself it is mid. It does not require concentration but as summons go it is actually rather weak

But I believe it has combinations with the related feats and with pact of the chain abilities if you cast it on an existing familiar which means it might have more spice.

The fact that it doesn't require
concentration is what makes it powerful. Plus as you mention there are various ways to improve it. Cast haste or enlarge on it. Feats like you mentioned. I'll point out that there are multiple ways for any class to get it. Also with Planar Binding you can make the Spell permanent. Maybe other things I haven't thought of.

If you cast Planar Binding on it, you can make it permanent.

Where are you getting all the resistances from?

Huh. Yeah, it would work. 1000 gold is a steep price, but perhaps in Tier 4 it makes sense.