For Dr. Kron, there are a few problems I have with it.
- As I previously mentioned, being able to use the effect of any DARK monster is something nothing should have. Instead, I would give it an effect that lets you temporarilly negate DARK monster effects.
- The effect that Special Summons it during the End Phase is unspecific. It implies you can summon it whenever you want during the duel, which is another effect nothing should have. Instead, I would go with an effect that Special Summons it from the Graveyard during the End Phase of the turn it's destroyed.
- If I understand the combo thing correctly, the xn (where "n" is a number) is a number of additional attacks, meaning Dr. Kron can attack three times per Battle Phase. This is another very strong effect that it probably shouldn't have. At most, I would give it two. Personally, I wouldn't give it the extra attacks at all. Regardless, I will show it with that effect in the other options below.
Overall, this is what I would go with. Other options are listed below.
Dr. Kron of Dark Matter
DARK
Level 4
Spellcaster / Effect
1400 / 1700
This card is unaffected by the effects of DARK monsters. This card cannot be targeted for attacks, except by monsters in its same column, but does not prevent your opponent from attacking directly. Once per turn: You can target one other DARK monster on the field; negate its effects until your opponent's next End Phase. If this card is destroyed by battle or card effect and sent to the Graveyard, Special Summon it from the Graveyard during the End Phase.
Other options for Dr. Kron :
Two attacks:
This card is unaffected by the effects of DARK monsters. This card cannot be targeted for attacks, except by monsters in its same column, but does not prevent your opponent from attacking directly. Once per turn: You can target one other DARK monster on the field; negate its effects until your opponent's next End Phase. This card can attack twice during each Battle Phase. If this card is destroyed by battle or card effect and sent to the Graveyard, Special Summon it during the End Phase.
Three attacks:
This card is unaffected by the effects of DARK monsters. This card cannot be targeted for attacks, except by monsters in its same column, but does not prevent your opponent from attacking directly. Once per turn: You can target one other DARK monster on the field; negate its effects until your opponent's next End Phase. This card can attack thrice during each Battle Phase. If this card is destroyed by battle or card effect and sent to the Graveyard, Special Summon it during the End Phase.
More difficult summoning condition, but negates the effects of all DARK monsters your opponent controls:
This card cannot be Normal Summon/Set. Must be Special Summoned by its own effect, and cannot be Special Summoned by other ways. You can send 1 "Juzzo" and 1 "Meth'hok" you control to the Graveyard; Special Summon this card from your hand. This card is unaffected by the effects of DARK monsters. This card cannot be targeted for attacks, except by monsters in its same column, but does not prevent your opponent from attacking directly. While this card is face-up on the field: Negate the effects of all face-up DARK monsters your opponent controls. If this card is destroyed by battle or card effect and sent to the Graveyard, Special Summon it from the Graveyard during the End Phase.
Juzzo only has two problems, and one of them is fairly small.
- Attacking Spell/Trap Cards isn't either a mechanic or an effect cards have had. What cards can have, however, are effects that destroy Spell/Trap Cards.
- Its effect that only allows it to attack Machine-Type monsters is extremely limiting. I would suggest removing it and either increasing its level (recommended) or lowering its ATK and DEF.
Overall, this is what I would go with. Other options are listed below.
Juzzo
EARTH
Level 6
Spellcaster / Effect
2100 / 2300
Once per turn: You can target one Spell/Trap Card your opponent controls; destroy it, and if you do, inflict 500 damage to your opponent. This card cannot attack the turn you activate this effect.
Other options for Juzzo :
Level 4
1400 / 1500
Once per turn: You can target one Spell/Trap Card your opponent controls; destroy it, and if you do, inflict 500 damage to your opponent. This card cannot attack the turn you activate this effect.
Lastly, we have Meth'hok. There are a few problems with it.
- The extra damage is unspecified. You need to specify how much damage is done by an effect.
- Treating something as though its in a differnt position is another mechanic that's never been done. This effect also doesn't have a working counterpart that easily emulates what you were going for. There isn't anything wrong with doing things that haven't been done, but the issue here is how other existing mechanics would interact with it. For example, cards in Defense Position cannot attack, unless it has an effect that says it can. Also, if it is attacked, we would need a ruling on if this card's ATK or DEF is used for damage calculation. To keep it simple, I would just give it an effect that switches it to Defense Position if it's attacked.
- 13 (or 12, depending on how your combo thing works) attacks is still overpowered, even if it only has 250 ATK. The reason for this is because of cards that change ATK. Unstable Evolution with this card basically gives you a monster with 2400 ATK that can attack 13 (or 12) times. The easiest way to fix this is to make it so Meth'hok cannot infict battle damage, but it does 250 effect damage when it successfully attack directly (which also links it to the burn effect you mentioned).
Overall, this is what I would go with.
Meth'hok
DARK
Level 6
Spellcaster/ Effect
250 / 2600
This card cannot inflict battle damage to your opponent. If this card successfully attacks directly, inflict 250 damage to your opponent. If this face-up Attack Position card is attacked by an opponent's monster, before damage calculation: You can change this card to Defense Postion.
I believe that should cover it. Don't be discouraged by the recomendations. You just need to try to balance the effects a bit more. Chances are, the ideas you have can still become balanced after thinking them over a bit more. It just sometimes takes a while. (I may or may not have spent 1 1/2 - 2 hours rebalancing these, which is far longer than I probably should have.)