Countermagic slows you down by roughly a turn for every mana it costs
Pokmon cards worth the most money overwhelmingly tend to be from the 90s, such as the iconic Base Set Charizard which has sold for as high as $420,000
Dark Magician of Destruction is the featured card
Additionally, Japanese sets are often smaller and more focused, while English sets tend to combine multiple Japanese releases
Most of the Fusion Monsters do have a side-effect of requiring specific materials but there are ways around that and some like Elemental HERO Core have more generic materials for easier summoning (in this case, only needing three Elemental HERO monsters)
However, if you want to get a little risky, you can ignore the Steel-type Magneton and slip in the Genetic Apex one instead