The Elements will Kill You (Added new Boss Monster and 2 Mages) [Good CnC will be repped]

[Valkyrus]

Sorry to say this, after so many apparently nice comments but in my opinion this archetype really wouldn't work well as a deck. It'd be slow and most monsters have much better real-life alternatives. Anyways, reviewing:

Eccentric Old Magician and Archmage's Apprentice have different names so they don't belong to the same archetype? (why?)
Apprentice is fine I guess (the wording makes it be untargetable by attacks even if it's the only monster you control though, since it IS an Archmage monster itself)

Old Magician is....weird. What do you need a level 7 Tuner for? I understand the  fact it's a Rank 7 Xyz Fodder, but your Set doesn't even have Synchro monsters. Besides nothing in your set would even be able to be synch-ed with this card (while level 7) since you don't have low-level non-Tuner monsters. (My understanding of a Themed Set is that the cards in it have some sort of synergy together.)

Fiso is plain bad (except for the art). The only good thing about it is that its targeted monster keeps the effect even after Fiso's off the field. But 500 LP is nothing. In a game where the same monster doesn't usually stay on the field for more than 3 turns, 1500 LP damage is the most you can hope for with this. I suggest making it 1000. Also, it should be made easier to summon. Having to tribute 2 monsters for this would always feel like a waste.

Isofa is also underwhelming. A level 4 or lower monster with the same effect and lower ATK/DEF would be good. This, as it is, isn't. And it also needs 2 tributes to be NS-ed without the option of it SS-ing itself somehow.

Lamara is also underpowered. Blackship of Corn does what she does, but better, and is way more accessible and easier to summon (also Blackship is an Extra Deck card which makes it summonable whenever it is needed. Unlike this.

Poisum is another  bad card. Level 7 and 1800 ATK? So what if it can do 1000 damage? So can marshmallon. It will hardly deal any more than 1000 anyway since its poor stats won't let it stay on the field for long.

The fusion's materials are too specific as well and you'll quite rarely be able to summon it. It doesn't need a Polymerization card, which is good, but the materials are still too many and too specific. You'll be -3-ing yourself with this. -2-ing at best if you manage to use his effect. If the materials are just "any 3 level 7 Archmage monsters" it'd be slightly better. It's destruction protection is also rather weak. It wouldn't be OP if it couldn't be destroyed by card effects and not be reliant on anything.

Now the Xyz might be the one monster you buffed a bit too much. Although it doesn't seem like a Xyz at all. Where is the detaching effect? Or you can
endlessly banish  backrow, gain LP and have it be a nigh-invincible 3000 ATK body for no cost? I suggest you have it detach 1 Xyz Material for each banishing effect and remove its "no target; no destruction" clause while it has no Xyz Materials, maybe have it be unable to attack as well while without mats (Something like Tiras, Keeper of Genesis). Also, maybe lower its ATK a bit. Maybe. You can make it just 2 level 7 monsters too. It'd be a nice generic Rank 7 alternative
 

As a whole, it's 5/10
it brings nothing new, most cards are random and you could barely tell they are from the same Set if they didn't have similar names.

Archetypes need to be able to work together and create combos easily. They should be able to Search (something none of your cards can do), should be
able to Special Summon themselves or other cards from the Set (something too few of your cards can do). Also, maybe have all monsters have 1 effect that all others do as well. Though, seeing as you're going for some sort of burn damage theme, then high-level high-ATK monsters should not be in it.
You either burn or you battle. Having both high ATK and burn effects is broken. Though as it is, the Set isn't broken (apart from the Xyz), it's just that it's not headed in the right direction.

You said you haven't posted your other cards yet so this is what I can say for now.
No hard feelings, it's just an honest review.

 

[Excalibur the Divine]

It's unfinished; I didn't add the synchro yet

[Valkyrus]

It's unfinished; I didn't add the synchro yet

Then why did you post the tuners if you have no synchroes ready? They have nothing in common with the other cards except their names anyway (even the name isn't consistent as I pointed out earlier). I honestly don't see how you'll be able to justify all these bad cards by giving them more support. Everything needs to be fixed.

[Excalibur the Divine]

You'll see