The land cyclers Eagles of the North, Lórien Revealed, Troll of Khazad-dûm, Oliphaunt, & Generous Ent:
Land cycling for 1 is extremely good rate, and these can fetch any non-basic land with the 5 land types. The effects on the front-side of the cards are very strong as well make the entire cycle an auto-include.
Rally at the Hornburg replaces Forbidden Friendship:
Now comes with 2 hastey boys!
Sulfurous Blast replaces Fiery Cannonade:
Now that's a blast from the past. The increase in cost is justified as 3 damage can just about kill anything on the board, including your opponents.
Drown in Sorrow replaces Arms of Hadar:
Losing the asymmetry is negligible. These type of cards are usually for control orientated decks. Your opponents will cry as this drops a turn earlier.
Dread Return replaces Disturbed Burial:
Murmuring Mystic replaces Moonblade Shinobi:
Murmuring Mystic eclipses Moonblade Shinobi as a repetitive token generator. While it requires you to be in a spell heavy deck it also does not need you to connect. Often times you'll find that it is difficult to return Moonblade to hand and perform multiple ninjutsu tricks a turn.
Phyrexian Gargantua replaces Girder Goons:
Same thing both give you card advantage
Lotleth Giant replaces Hezrou:
Does a better job at finishing the opponent off. Hezrou tries to assist aggro decks in getting hte last points of damage, but burn is just much better.
Demon's Disciple replaces Fleshbag Marauder:
(there's no common pw yet...)
Shipwreck Dowser replaces Mnemonic Wall:
Steer the deck to be more aggressive.
Ministrant of Obligation replaces Sandsteppe Outcast:
Lembas
Cast into the Fire - If artifact recursion becomes too pervasive, then we can substitute Abrade with this.
Generous Gift - This gives a little too generous of a gift for this format. Often times an upgrade.
Crawling Infestation - It's interesting to say the least, but the restriction to produce insects bugs me enough to not include this.
Vizier of Tumbling Sands - If only there were combos that we could capitalize the fiddling effect with.
Cryptic Serpent - Tolarian Terror at home.
All that Glitters - While a really powerful effect and making waves in pauper constructed, it's really not all that impressive in limited. Ethereal Armor would be reintroduced before this gets added.
Guttersnipe - This would be a fantastic pay-off for spells decks, I just don't see there being room at the moment for this.
Rapacious One - A fantastic effect, however our 6 drop slot for red is full of creatures that can deal with the board or provide better utility. I can see this pairing very well with Impact Tremors.