While Brown found the Friend uninteresting from a chess-problem standpoint, I think it has great potential

It seems to me that, especially in these larger numbers, the friend may work much better in games than problems for the same reason that the Orphan and Joker are perhaps more suited to problems: they lack the interplay between the sides, and thus the owner has actual control over their deployment. Orphans and especially Jokers would need enough sufficiently mobile pieces on the board that it's hard to avoid granting them power (somehow not unlike Contramatic Chess. Hmmm…)

Any sliding piece — Archer, Caliph, Lady in Waiting, Mtawala, or Sniper, as well as a Friend trying to use their moves

…or fellow Bodyguard?

A Friend only gets the special initial moves of a Pawn if neither the Pawn granting the ability nor the Friend has moved yet (meaning it can only be done with the help of another Friend).

But how would that other friend get there? Surely if it got there on its own volition it would be considered to have moved, meaning can't have and therefore can't transmit the initial Pawn moves?

Does a Squirrel Displacement not count as movement for the piece being displaced? That would solve this, though it'd also make it possible (indeed necessary for the chain) for a Friend to gain the initial moves directly

the Friend can also receive […] the Displacer Squirrel's ability

So to be clear (purely for my benefit, as I was thrown the first time I read it), the Squirrel can still capture enemy pieces normally?

the Friend can also receive […] the Poison's poison

Iow a Friend captured whilst under the guard of a Poison annihilates its attacker? Is this optional (in the rare case, such as blocking check(mate) that waiving it would be desirable)?

Similarly, are rifle‐capture and/or withdrawal optional, if the friend is also borrowing from a piece that can make the same move w/o the special power? And (if only for completeness) what about Hia power?

gain[ing] moves and abilities from another Friend […] isn't necessarily reciprocal

This is a nice detail, which I'd missed in mỹ own thoughts about this piece. It'll be hell to keep track of though, especially if the false guard is by a third or fourth friend

Any piece adjacent to a Jellyfish cannot move, including leaps, slides, and rifle captures. However, unlike the case with the Bodyguard, this does not affect pieces merely moving past the Jellyfish

I've been meaning to put together mỹ own showcasse game for the (in my case catch‐only) Bodyguard (it's a really nice piece) and was likewise going to include a traditional immobiliser — I find the duality between a piece that impedes long range movement but allows escape and one that completely traps things but allows passers‐by quite pleasing :‌)

Normally, the Friend doesn't gain any of a piece's "special moves" at all, and under Mr. Brown's rules presumably wouldn't gain any special abilities from other pieces either. I've altered that rule for this game; pieces like the Bodyguard, the Displacer Squirrel, and the Jellyfish are here specifically to explore the possibilities.

Strictly speaking, having gone hitherto entirely unused, there's no precedent at all here, and I wouldn't be surprised if Brown's Orphan problems also lack other pieces with special abilities, leaving no precedent there either. And even the Joker, while more popular, tends (I can't recall any exceptions offhand) to be paired only with relatively orthodox pieces…

Of course the interaction of special powers with Orphans and esp. Jokers is substantially more complicated (what does it mean for a joker to imitate Hia power? Not that I don't have mỹ own interpretation…). We'll have to leave that for a notional ‘Grand Imitator Chess’ — I'll certainly give that a go eventually

I have to say I like this a lot. It's a shame it looks like a nightmare to programme; looks like playing it would be a fascinating experience :‌)