Sea Monster decks will love this, and with all of the draw-on-combat-damage effects in blue and green, getting some cheeky unblockable Fish is pretty good, actually
The short answer is that if you are paying more to kill a single threat card than that threat card actually cost to play you will often end up falling behind
Trainer - There are multiple different types of trainer cards (items, stadiums, and supporters) that a competitor can use during a battle
The flipside, an enchantment saga aptly titled The Great Work, deals damage to each opponent and their creatures, creates some Treasure tokens, and has the chance to cast a bunch of spells out of your graveyard
10 Malfegor Malfegor is a Demon Dragon, and thats awesome
With the right deck, Past in Flames can enable incredibly fast strategies that go off in early turns