If you play an Ally "at no cost", you don't pay the additional costs, right ?

I think a fun use for Motivational Speech is to play Summoned Hound: as you don't pay costs, you don't have to add Unbound Beast in your deck, and therefore you have only the advantages of the ally.

It allows you to simply play the Hound instead of trying a way to get it in play without playing it (for example discarding the Hound and then playing A Chance Encounter).

For Charlie Kane, you can even use the Hound twice:

• exhaust the Hound to start a Fight / Investigate action,
• exhaust Bonnie Walsh to get a +3 (so you have a skill value of 8),
• ready the Hound (with the on Bonnie),
• exhaust the Hound to use it a 2nd time.

This version of Hastur is a Massive punishment for 2 - 1player just for taking the doubt option. The scenario turns out a hell in that situation. The other two versions are waaaay softer compared to this. For such a good campaign as Carcosa is, I consider this card its only flaw: Nearly impossible to beat doubt mode in 1-2 players mode no matter how well you played the campaign. And you find that out at the end.

An obviously great choice with Eyes of the Dreamer & Breath of the Sleeper but the really spicy combo I'm surprised nobody has mentioned yet is having Spectral Shield repeatedly eat the 3rd charge off of The Red Clock to take 2 additional actions every single turn!

That's 2 Leo De Luca's with even more soak than the Leo's would normally provide all for 1 action, 2 cards, 3 resources, 10 xp and an accessory slot assuming you can find 1 damage or horror to soak up every turn. The most obvious choice would be to drop the Spectral Shield on a Guardian's Beat Cop or Field Agent. Alternatively, if there happens to be an Internal Injury or Chronophobia in play, your team can laugh off the fact that not only did a basic weakness just get cancelled out but also became a combo enabler in the process. And barring those more convenient options, you can always toss the shield on yourself and just run a copy or two of Forbidden Knowledge to give yourself a useful self-horror outlet for those turns you would otherwise struggle to find an enemy or treachery to hurt yourself with (which serves as a not half-bad excuse to run Adaptable so you don't actually have to put the Forbidden Knowledge's in your deck until you've purchased the Red Clock).

Theoretically, anyone with Rogue 0-5 access can run this combo using Versatile. Of course, Jenny Barnes can do it by taking the Shield as part of her splash. Though the best choice by far is Sefina Rousseau, who can not only run both Red Clock (5) and Spectral Shield as part of her normal deckbuilding options but has a better chance of seeing the clock and shield early with her 13 card starting hand. And she can keep the shield fed by utilizing a full array of charge based Mystic spells. That's important as the one downside to this combo is that Spectral Shield is not an optional effect. You MUST spend charges if any are available to be spent which means you'll likely want a secondary asset with charges to pull from anytime the Shield ends up eating more than 1 charge per turn.

The main, general-use purpose of this card is to gain resouces while killing your Arcane Initiate, David Renfield, or other Doomed Ally so their doom diesn't cause the agenda to flip early.

You can hope to kill them in other ways during the Mythos phase, but this just makes it a bit more guaranteed

I believe using Robert to play a Remington Model 1858 will net you two free shots if you chose to play it. (I'm not entirely sure if it gets you a 2nd free shot if you discard it, as it hasn't 'entered play'?) In any case he's great for a Fist-based gun fighter rogue. (I'm guessing he was designed to be Michael McGlen's friend, but he seems quite helpful to Tony Morgan too.)