Fitz is a bad design, in my opinion. Legends aren't good for throw-away effects. Lieutenant Kirtar is probably a golden exception to the rule. Not something you make a habit of. Feels like it's modeled after Kim Jong-Un. lol at believing he's not highly sentimental to his company. Consider an more enduring concept. "As long as Fitz attacked or fought a creature during your last turn, other players can't become the monarch."
The Fool has big shoes to fill. Not entirely certain that it lives up to the demand. It is a great ability and all. The Fool is definitely a Rogue at least, and certainly not a Shaman. It should also have black in the color. Not sure how you would fancy that at the current cost without it becoming incredibly polarizing. Three color would help it live up to the aspirations for embodying such an iconic concept.
Althea is a good concept. Not really much to be said about it. I don't really like Menace. At least, I think it's way abused in development.
Kennit is kind of useless. You probably can't afford to pay the typical amount of life. For a 2/2 with only that ability, it's a little too color heavy as well. As far as flavor justifications go, that's all your style. Nothing can really be said there. I would probably consider something like, whenever an opponent loses exactly 1 or 2 life, you may draw a card. That would be great.
Tintalgia is neat. It's just a little overcosted. The effect itself can be taxing to pull off. I understand that it's a dragon. Even a 4/3 or a 3/4 is incredibly powerful.
For reference, Reap has repeatedly said that he hasn't played Magic in 10+ years and thinks the game is bad, so most of his advice is not worth listening to.
Fitz is mostly fine and actually fits (hehehe) pretty well in Jund colors, the fighting being red/green, death trigger for monarch feeling black, ward in green. The repeatable fight is strong, but since it opens him up to dying to pretty much any blocker it isn't too powerful.
I don't see any white in the Fool's design, this is easily a mono-red card, though probably needs to be 3-4 mana to be balanced with other redirect abilities.
Althea's payoff isn't worth the cost of giving up a permanent: Best choice is to give a land since that's hard for them to get rid of, but that sets you behind effectively two turns to do so. Also she should be a Pirate.
Kennit will be ridiculously strong. Like, Yawgmoth's Bargain strong. The drain and lifelink already in Black is just the icing on the cake, but this card will be a rival for Griselbrand in some decks.
You should specify if you want Tentaglia to trigger off herself or not, either "Whenever another Dragon enters the battlefield..." or "When Tentaglia or another Dragon enters the battlefield..." Also needs to specify "enters the battlefield under your control..." because, as written currently, I gain control of a permanent when my opponent's dragon comes into play (and probably that dragon is what I gain).
If it only triggers off other dragons, its fine at 6/6 for 7 - on par with Utvara Hellkite. If you get a steal of it entering then it needs to come down 1-2 power and toughness each - see Dragonlord Silumgar.
I don't know the characters well enough to comment on how your designs match flavor, but theres at least some interesting card designs here.
Fitz having a death trigger is definitely a nod to the novels. Agreed it shouldn't be overused but I think it's appropriate for the character in question. I don't love the idea of a card that interacts with the monarchy without granting it but I actually really like the idea of him denying the monarchy. That's probably a better fit for his flavor. Might tinker around with him for a bit.
While ~ is on the battlefield you cannot lose the monarchy.
When ~ dies you become the monarch.
When ~ attacks you may have it fight target creature.
Now we have haste for his recklessness, defending the monarchy for flavor and a black concept (greedily protecting the monarch) and then fighting to capture his berserker nature and recklessness in one.
I should have given The Fool a subtitle or gone with Beloved, The Fool as the card name. He's definitely not the concept of the fool, but a jester/fortune teller specific to these novels who goes by "The Fool". Unlike the broader concept he definitely doesn't fit the black section of the color pie at all being a character defined by selflessness or at least continuously choosing selflessness against his wishes. I considered the creature type shapeshifter but it's not quite right. Rogue might work but it would have to be rogue and shaman because he is defined by his branching visions of the future and trying to alter which path the world takes.
Kennit is definitely in a weird spot right now. I was trying to capture his masochism and greed but I didn't quite hit the right design.
Maybe he could be a BB 1/1 with the same ability. That would have him come down earlier and be more likely catch early in the game damage. Plus BBBB is a really ugly mana cost to not be a super flashy card. I like that sometimes it will be a huge risk to choose to draw the card and that you often won't be able to. Sort of an aggressive take on Ad Nauseum rather than a combo one. My main concern would be is it too good with blood artist style of cards.
I was basing Tintaglias's cost on Agent of Treachery. She's a bit more narrow in terms of stealing though but has better stats and a tribal benefit. Felt like a reasonable tradeoff. Plus I'm old school and think non baby dragons should be expensive.
@Rowan Thanks for your feedback too. The white was in mind mind for flash (and flavor). I always forget it's technically in red's color pie for creatures. Would it be reasonable at 1WR mana or is that still too pushed? I'll have to try and think of something to make the card more white. Definitely want it to be a WR card but need to rework it mechanically.
Althea was definitely designed to be a bit of a johnny card. Similar to a harmless offering effect. Just a bit off kilter to get the creative juices flowing. Though maybe too aggressive in effect to be interesting to Johnnies. As for being a pirate or not I'm a bit torn on that for flavor reasons. She sort of eventually becomes one but most of her journey is defined by hating a pirate and working to stop one. She's a sailor but not a pirate really.
And wow. I completely missed the mark on kennit. I thought tying it to opponents life loss would make it nowhere near those cards, but if it's drawing those comparisons I clearly completely misjudged him.
And that makes sense on Tintaglia. Definitely wanted a trigger on herself as well as other dragons. Too pushed with the haste though. A 4/4 probably makes more sense.
~ cannot attack or block unless a creature has died this turn.
Whenever a creature you control dies ~ gains your choice of flying, trample, lifelink, or vigilance until the end of turn.
Verity, King-In-Waiting 1WU
Legendary Creature - Human Wizard
Vigilance Wt: tap target creature. 5UU: gain control of target creature.
Burrich, Heart of the Pact 4WG
When ~ enters the battlefield create 2 1/1 white dog tokens.
Dogs you control get +1/+1 and have lifelink.
I know wotc doesn't use shroud anymore but I pulled it out for flavor purposes (he's sealed from the telepathic magic in the novels both friendly and hostile). Preventing flicker shenanigans is just upside in costing him slightly more aggressively.