From the downright invincibility of Blue-Eyes Chaos MAX Dragon and the unparalleled disruption of Herald of Perfection or Herald of Ultimateness, to the one-sided Giant Trunade and Chain Energy combined into Odd-Eyes Gravity Dragon and the entire phase skipping of Amorphactor Pain, the Imagination Dracoverlord, these Ritual monsters are very powerful, yet require considerable setup to achieve and summon
Early on you'll want to prepare the cards like Close and [EX10-069 Unique Emblem: Gravel Hearts] so you can digivolve into Magneticdramon
While Gyarados EXs Rampaging Whirlpool discarded a random Energy from any of the Pokmon on your or your opponents playing field, Mega Gyarados EX discards the top 3 cards from your opponents deck
There are all kinds of wild effects here, though there are usually very few phenomenons in a planar deck, so you don't have to worry about it too much
It commonly works as a poor Timetwister when you discard it or mill it
Day of Black Sun is one of the early highlights of Avatar for Commander, so this is a fine pick for a promo card