In context of solo play Roland is very solid pick because his statline and cardpool allows him to get clues as well as deal with enemies. Roland´ ability is basicially a once per round use of evidence which can be used to clear clues of high shroud locations which he is unable to investigate with cards such as Flashlight and Magnifying Glass. This becomes especially important in solo play there the presence of enemies usually means that you need to waste actions on dealing with them. However, in context of Roland´s ability the presence of enemies is beneficial as they can be used in order to make progress towards the act deck. This theme is further developed by cards such as On the Hunt which spawns enemies at your locations and Scene of the crime which profits from the presence of enemies at your location.

Roland´s glaring weaknesses are his low willpower and sanity. Roland´s willpower of three makes him vulnerable to nasty willpower treacheries and the existence of encounter cards which can deal up to three (or even more) horror means that Roland is prone to go mad during the course of a scenario. What makes this situation worse ist that Roland´s unique weakness Cover Up forces you to either waste time in order to get rid of the clues on it or to take a mental trauma which makes it even more likely that Roland will go insanse.

While these weaknesses were huge problems at the beginning of the game when there were not a lot of good ways to deal with them, the growing card pool has mitigated them more and more: the dunwich cycle introduced cheap expendable allies such as Art Student and Dr. William T. Maleson who could soak sanity damage and provided additonal benefits for Roland. During the Path to Carcosa cycle Roland got access to cards such as Forewarned and Logical Reasoning which provided him with even more ways to deal with nasty treacheries or heal horror. At the same time Roland also got access to more and more cards which allow him to place clues on locations such as Quick Study from the current Forgotten Age Cycle. These cards allowed Roland to place clues on locations in order to mitigate a situation in which Cover Up came up and there were no collectable clues in play. All of this in mind I think Roland is a very beginner friendly investigator who allows you to play a guardian who contributes not only in regard of slaying the beasts of Arkham but also in regard of clue gathering.

I think this card is gaining new life after the introduction of the M1918 BAR. Sure, it's ain't cheap. But in curent cardpool only 2 investigators can use this combo. Leo Anderson, who has access to a Lonely Wolf and Hot Streak(2), and Zoey Samaras, who gain resource when engage the enemy (and She can use Lonely Wolf as well). I finds M1918 as an excellent card for both trash mobs and bosses, but it requires a different approach than Shotgun or Lightning Gun. Both Venturer, and Extra are Ammunition pretty bad for M1918 BAR, and without Contraband, this card will not show its true potential.

Most people think guns when they think about this card, but imagine Rex Murphy pulling Strange Solution (Acidic Ichor) out of his sleeves, dealing 9 damage, and be ready to play that card normally the next round! Also great with a Flashlight.

This card seems incredible at first glance. And it really is.

+2 damage is a dominant effect in this game, and cards that offer repeatable +2 damage are almost always outstanding. (Springfield M1903 is why I had to say "almost".) Compared to the other +2 damage weapons in the game, Acidic Ichor is way cheaper and more convenient. Think of Lightning Gun; Acidic Ichor is cheaper by 1 XP, 5 resources, and 2 hand slots. That's amazing. It's kind of bizarre that the faction that's the best at finding clues would get a combat card as sweet as this, but that's how it is.

Yes, you need to identify the solution. But that basically boils down to spending a couple actions and passing an Intellect (4) test. Even on high levels, that's not much hassle.

As icing on the cake, Emergency Cache III is a quite efficient (albeit XP-intensive) way to reload this card.

So what's the catch?

Well, on lower levels, I would say there really isn't one. On Easy, Acidic Ichor will basically perform like a much cheaper Lightning Gun. That's every bit as good as it sounds.

On higher levels, though, and particularly on Expert, Acidic Ichor is no Lightning Gun. This is because attacking at base 6 is nowhere near enough. If you try to hit a 4-fight enemy without boosting (and most good targets for this card will have high fight), your odds of hitting are going to be substantially under 50%. You need to be able to boost your shots by a good +3 or +4 to make this card rewarding. Since Seeker decks tend not to be naturally loaded with Combat icons, that's not always easy.

Of course, you do have some options for getting that Combat up. You could run Overpower, Inquiring Mind, Unexpected Courage, maybe even Scientific Theory. Minh (easily the best Seeker at running Acidic Ichor) can take Lucky!, which helps an awful lot. Daisy might be able to get Encyclopedia to work out in certain situations. Maybe your allies have the spare cards to boost you. You have options. But it's difficult enough to hit with Acidic Ichor that the card is no longer a slam dunk.

I think Acidic Ichor becomes more of a build-around card on Expert. It's not something you can just throw into any Seeker deck and get good results. If you're in a multiplayer group and your allies are doing a good job handling monsters, devoting a lot of deck space and XP to Acidic Ichor may not be worth it. It can absolutely do great work on Expert if you put the effort in, but you do have to put the effort in.

I believed this was a great card. I made the huge mistake to use it instead of Unexpected Courage

Location with clues are indeed plenty during the game, but what is the purpose of the Seeker class ? Empty them. And when it's empty, this card is a dead weight in your hand. You'll have to pay attention not to end your turn on an empty location, which requires too much planning and is often counter productive

Unexpected Courage will be enough in 80% of times, while half the time, Inquiring Mind will be completely useless, often at the wrost moment (Encounter deck draw)

Maybe in addition to 2 copies of Unexpected Courage, but even then, I'm not convinced.