Dungeons can be accessed when a card has the phrase Venture into the dungeon on it, and has you journeying through different iconic D&D dungeons: Tomb of Annihilation, Dungeon of the Mad Mage and the Lost Mine of Phandelver
Either way, a 3/4 Flying Lifelink for five that can resurrect creatures every time you go to pass the turn is phenomenal
5 Argomon and Blossomon, coming in at $0.20 and $0.70 respectively, are also viable options, as their download effect can make them much easier to get on the field for cheap
(2) If this card is Normal or Special Summoned, or flipped face-up: You can banish 1 Invoked monster from your Extra Deck
It can attack directly this turn
This allowed us to design cards that people could main deck but normally wouldn't