See a complete list of the Additions and Subtractions from Fourth to Fifth Editions
For example, if you're instructed to draw two cards and you replace the first draw with a dredge ability, another card with a dredge ability (including one that was put into your graveyard by the first dredge ability) may be used to replace the second draw
This card has many potential applications, but in order to keep things brief, lets go over the highlights: Generates multiple uncounterable creatures that get huge in the right decks Tutors for key artifacts such as Colossus Hammer, Shadowspear, Nihil Spellbomb, and Mishras Bauble Provides enchantment and land card types for delirium Provides a powerful late game engine when paired with Wrenn and Six Youll find Urzas Saga most commonly in Hammer Time, Jund Saga, Amulet Titan, Hardened Scales, Affinity, and Eldrazi Tron
Probably helps deter tourists
Some of the more traditional creature types, such as [c]Elf[/c], [c]Goblin[/c], and [c]Merfolk[/c], have many cards that encourage you to focus exclusively on one creature type