Like most Pokmon cards, the value of Magneton depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Skyridge)
Your second example for properly summoned monsters does not work because it is not possible to attempt to Fusion Summon Sea Monster of Theseus outside of a chain, and you cannot use Solemn Judgment (or any card or effect that negates summons) to negate the Summon of a monster that was Summoned during a chain
Listed as the WORLDS WORST CHARIZARD GOLD STAR EX Dragon Frontiers 100/101, and originally priced at a somewhat optimistic $911, the entry made no bones about the state of it
Illustrated by Madeline Boni Standard Legal Alchemy Legal Pioneer Legal Historic Legal Modern Legal Brawl Legal Legacy Legal Comp
C Common Groza, Tyrant of Thunder X DARK Level 8 [ FiendSynchroEffect ] ATK 2800 DEF 2800 1 Tuner + 1+ non-Tuner Fiend monsters During your opponent's Main Phase (Quick Effect): You can target 1 Effect Monster on the field
Perfect synergy Tokens, life drain, and devotion all weave together into a terrifying control engine
