Summon Beast magic item interaction question.

[ShadeRaven]

Hey there. Quick question about the rules interaction in this specific case.

I am playing a ranger/sorcerer who just got his hands on staff of power (relevant rule text: While holding it, you gain a +2 bonus to Armor Class, Saving Throws, and spell Attack rolls) and an Insignia of Claws (relevant rule text: While wearing the insignia, you gain a +1 bonus to the attack rolls and the damage rolls you make with unarmed strikes and natural weapons).
If equip the bestial spirit summoned with the summon beast spell with the insignia - what will be his melee attack bonus?
According to the spell it is calculated by my spell attack modifier.

Would the equiped on the beast Insignia of the Claw add to that?
Would the Staff of Power attack bonus be applicable?
Would both bonuses stack for +3 bonus to the spirit's attack rolls and +1 bonus to it's damage rolls?

[Dualight]

I am not familiar with the Insignia, so I have to know first: Does the Insignia require attunement?
If it does, it won't work with the beast, as you would have to attune the beast to the item every time you cast the spell.
The staff of power does apply, so the +2 on attack rolls should apply to your summoned Beast.
If the Insignia requires attunement, since you mentioned being a sorcerer, there is a way to have it apply to the beast, if you apply the Extended Spell metamagic.

It takes a short rest, which takes at least 1 hour, to attune to a magic item, and summon beast has a default duration of 'concentration, up to 1 hour', which becomes 2 hours with Extended Spell.
So, if you know that you will get into a fight in less that two hours time, but have enough time to take a short rest before combat begins, you can summon the beast with Extended Spell applied, have the beast attune to the Insignia over the rest, then go into combat with the buffed beast.

If you manage to get this convoluted setup in place, the you should get the full bonus, unless your DM rules that the maul attack action isn't a natural weapon, or decides that summoned creatures cannot attune at all.(RAW any restrictions on attunement are item-specific, other than being physically capable of operating the item, if it needs active usage, like a weapon, but it is a reasonable house-rule to make summons unable to attune if they will be gone at most an hour after attuning to the item.)
If the Insignia does not require attunement, then it should be able to apply, assuming that being worn is the only condition for receiving its benefits.

Do you know where that Insignia comes from(that is, where would i be able to find the full information)? I am curious if it is homebrew or official material, but from a book I do not have access to.

Finally, all of this is my reading of the RAW, there is always the possibility that your DM disagrees. And even if the combo doesn't work RAW, you might still be able to convince your DM to let you do it anyway. It is a clever idea, whether it works or not.

[ShadeRaven]

Do you know where that Insignia comes from(that is, where would i be able to find the full information)? I am curious if it is homebrew or official material, but from a book I do not have access to

We got it from some crazy half-dragon cultist lady by the end of the Horde of the Dragon Queen adventure. I believe it is an official item, since my DM is not much into homebrewing. It doesn't require attunement.

[Dualight]

Since it does not require attunement, the combination should work, unless your DM rules that the spirit's attacks do not qualify, which would be a stretch.
You will have to equip the insignia to the spirit every time you summon it, since it disappears at the end of each summoning, so it won't appear with items pre-equipped without your DM's support.

Still, it seems like you lucked into a good combo of items there.
In summary, the interactions work as you suspected.
I hope that your question is now answered and that you will have a fun time with your newly-empowered buddy.

[Valmark]

The issue with the staff of power is that the spirit doesn't have proficiency with it nor does it often have hands or equivalent to properly wield it- your damage might drop more then it increases.

Insignia seems like it'd work once you can get enough time from Summon Beast to let it attune and still stick around.

[Amnestic]

Would the equiped on the beast Insignia of the Claw add to that?
Would the Staff of Power attack bonus be applicable?
Would both bonuses stack for +3 bonus to the spirit's attack rolls and +1 bonus to it's damage rolls?

Yes to all, three, so far as I know, unless there's a specific exemption in the items or they're the same item (you can't benefit from two staff of powers at once). In this case that doesn't apply to either IoC or SoP, so you're good to go.

[Chronos]

The Staff of Power only applies to spell attack rolls. What are you summoning that's making spell attack rolls?

[Amnestic]

The Staff of Power only applies to spell attack rolls. What are you summoning that's making spell attack rolls?

Summon Beast (and indeed all of Tasha's summon spells) use your spell attack modifier for their attack rolls.

[Chronos]

Ah, OK, I'm not familiar with Tasha's; I didn't realize they did that. Then yes, the combination looks to be legal.