(Please be aware I'm talking about 5.0 here. Everything I say here is wrong for 4.0 and 3.5, and I don't know anything about the new edition.)

It's a little complex.

5e wasn't really designed for multiclassing, the original intention was to disallow multiclassing altogether, and the feature was only added last minute after playtesters complained. They didn't really try to balance it other than trying to make it weak enough that most players would be dissuaded from taking multiclass levels.

The main cost of multiclassing is that it delays your class features for a level, for some classes, such as primary casters, this is a big deal - a wizard doesn't want to wait until level 6 for fireball. For other classes such as rogues and monks, they might not really care as much about higher level features. Once a rogue (played by a player who is minmaxing for power) has reliable talent, they often multiclass into something that'll give them new features (Paladin is quite popular as it increases your damage, gives you a better hit die, and adds new spells and abilities.)

One of the biggest reasons to multiclass, or refrain from multiclass is roleplay - as this is entirely based on a character's narrative and the story being told, the consideration of whether or not to multiclass for story reasons is essentially a personal choice.

For players looking to maximize their power, it's important to consider whether the features you'd be taking in your new class are useful in your campaign. I mentioned Mask of Many Faces, but that's a useless ability in a pure dungeon-crawler style "fight a new monster each week" style campaign.

It's also important to think about the scope of your campaign. Many people look at the level 20 capstone abilities, which can be extremely powerful, and will argue that multiclassing is never good because it locks you out of those abilities - but consider how long you're going to be playing your character and at what levels. Most campaigns that even get to level 20 wrap up after a couple of encounters, so is that exceptional power, for two sessions, better than taking a new feature that will last you for tens of sessions?

Most character classes, especially martials are very front-loaded. The first 5-10 levels contain most of the core features of your class, and before you've unlocked those, it's often tough to justify multiclassing - but once a monk gets access to stunning strike, do they care about other Ki powers? If a campaign is planned to end on an even level, does a full caster care about that last level when they're not getting any new spells?

As a very very rough rule of thumb, full-casters often want to avoid multiclassing altogether, or if they do multiclass, they want to take a single splash level of another class once they have the spells they care about. For most of those classes, that's either level 6 or level 14. Martials are often more flexible, as higher level features often amount to more choice in abilities rather than mechanical power. Swapping to a different class offers different choices, and certain builds can by synergistic.

Rangers always want to multiclass, because ranger sucks. /j

One level of warlock buys you eldritch blast and mask of many faces.

One level of artificer buys you the ability to cast cure wounds with your spellslots, and the ability to use medium armour.

They're real popular splashes.

I did a little digital trickery to make this work. It'd be possible to try and do it with blending pencils, but for a daily drawing challenge I figured it'd be a lot faster to draw the reflection faintly, and then chop it out of the image and add it as a transparent layer.

I'm happy how well it worked!

It's close to her record.

Here's a bonus Konsi

Addis explained in an earlier strip - the people making the accusations are not interested in whether or not the accusations are true, they're interested in manufacturing a scandal.

When people with an agenda are pushing conspiracy theories, there is no test or proof you can administer that will satisfy them. They will just move the goalposts. "She found a magic way to cheat the zone of truth, that's how awful she is." "She's so corrupt she doesn't consider what she did to be cheating." "The church cheated for her and she didn't notice". "The person casting Zone of Truth is part of the conspiracy."

I think the only 7 in here is PIGFEED. There's an 8 which is almost certainly the OP's joke.

the odd stop signs told us to stop, but the even stop signs told us to stop stopping.

Fortune's favour would be pretty useless in this kind of situation, as it takes a minute to cast, you can't subtly re-up it during the game. You could pre-cast it and get one favourable outcome, but that's not enough to win a tournament with, and the 100gp cost would mean you're probably just wasting money. On the plus side, it's not concentration, so you could put the buff up on top of enhance ability or borrowed knowledge.

As for the house rule, what's happening here is tomfoolery and japes.

As for Konsi's access to this spell in specific, most of the spellcasting NPCs in our setting were created and had their spell lists defined early in the campaign. EGtW came out after they were already long established - the party actually knows Addis' spell list (it's a static list, consisting of a subset of the full cleric list). Konsi's sudden acquisition of a new luck-based spell, as an outcome/reward of her completing a major goal of her goddess, does make some kind of sense as a "special" situation.

As to whether or not Konsi is a "chosen" it's a little ambiguous. Tymora already has a defined chosen in canon (Curran Corvalin.) Gods normally only have one chosen at a time.

Tymora hasn't explicitly made it clear to Konsi that she's chosen, just that she has a mission to fulfill, favour and support. Likely, Konsi's on the path to becoming Tymora's chosen, but she's not there yet, she's just an important priestess that's going places.

As October has recently passed, here's a bonus Konsi

For DnD, I normally aim for six players, and I run if there's at least four present.

Knowing that the game will go on anyway without you is really good motivation to not flake out (I speak as someone who flakes out a bunch.) - and DnD is a very easy game to just have someone be not present for a week.

One time I built an arena out of kinetic sand, with shaped obstacles and dunes and stuff, then scraped a grid into it for battle. I built some working pit-traps into the sand itself that only collapsed with enough weight was placed on them, and I glued small weights to the bottom of the player minis to trigger the traps, while using light plastic kobold minis for the monsters, which did not trigger them.

The next week my girlfriend responded by running her game with a functioning sewer system with variable water levels.

alright, I'll send her over...

Kyrzin's Ooze

This is very much a non-canon Konsi. Konsi would be a fuzzy/happy/sleepy drunk, rather than a grumpy drunk. Once she gets tipsy she just wants to snuggle.

Also, she's immune to all poisons.

As usual, have a bonus Konsi

Yeah, it's ambiguous. I interpret the "you can be one foot taller or shorter" to mean you, and something like a hat or ridiculous hair can just be as large as you like so long as it still looks like an item of clothing and not (say) a billboard.

Of course, at very large sizes, something's going to clip into the illusion every now and then, so it'll obviously be an illusion to anyone who is around it for more than a few minutes. I'm imagining small birds trying to land on it and faceplanting into your head.

I suppose y'all can have a bonus Konsi, as a treat.

Okay, it should be working reasonably now, hopefully what we've done will be robust enough to take us to the server move.

We've been having server issues for a while, I know. The main culprit has been a massive increase in scraper bots that effectively serve as a DDOS on my site. Long term they should be solved by the upcoming server migration that's coming, but that's a long and slow process.

I think I have a stopgap solution this week that should get it up and working well... it's not cheap but I'm willing to put some money into making sure people can read the comics.