I need help with the script for these cards:







I would write the effects here but they're reasonable to read from the image

No man, I get to tease you with proper psct, and then, maybe someone else can help .

Life & Death
1 LIGHT Fiend-Type tuner + 1 non-tuner DARK Fairy-Type monster
Must be synchro summoned, and cannot be special summoned by other ways. This card cannot be destroyed by battle. This card returns to its owner's extra deck (hand, it's not possible yet, at least I'm sure ppl here have tried, to treat extra deck monsters as main deck monsters, though) during the end phase of the turn it was summoned.

Now the rest of the effects I really don't know.

This card can attack all monsters your opponent controls... multiple times I guess. Like if the opponent has a marshmallon in defense mode, you can attack into it multiple times even though it accomplishes nothing .
Limit it to once each IMO, otherwise if they have like an amazoness queen or something of the like in attack mode, you could just attack it over and over and that's just not fair :S.
All of what I said doesn't matter though because the next effect makes it so you can only attack once with it anyways.

(After damage calculation), if this card attacks: change it to defense position. With the way you had it, you'd never get an attack through, making the next effect completely useless 

(After damage calculation), if this card destroys a monster by battle: send the destroyed monster to the bottom of your deck instead of sending it to the graveyard and if you do, send the top 2 cards of your deck to the graveyard... or remove them from play is the one you were probably going for.

This card's ATK and DEF are equal to the amount of cards on the field and removed from play x 100 (Max 10000)

Crescent
Not sure if it's possible to override the gemini mechanic with another one to enable a gemini monster. In all honesty, I haven't played around too much with geminis.

Level as another level (on the field I assume) I usually see with just monsters that can be treated as a certain level for xyz summons. Not always. But I believe it is possible. It'll just look ugly when you hover over it.

First gemini effect is fine, just copy fire princess and change the condition

2nd gemini effect, that's not how it works, gemini effects reset off the field. It'd have to be just a regular effect I believe.

Mephist
1st effect, kind of a cheap effect ;s. summon gets negated, you still go plus

1st effect is fine worded how it is, but as far as scripting, self destruct effects have never needed functions. The discard effect might not be possible, or what'd happen is both players would discard before it dies. Not exactly sure. It might just be easier to have it resolve on a chain.

2nd effect also ok worded how it is.

3rd effect also fine how it's worded.

Life & Death you really should look at again. It's a bit confusing so ppl might not script it the way you expect :S

Thanks and okay!