Several things I found interesting for a retrace deck:
Retrace cards (duh), mainly red/green eg.:
Calll the Skybreaker
Waves of Agression
Possibly more lands than in a ususal deck, maybe 28 or so.
Some of these lands are in form of karoos, so that you can tap a land for mana, bounce it when you play a karoo (essentially increasing its productivity by 1 next turn), then discard it to retrace.
Life from the Loam adds a mice touch, returning lands from your graveyard to retrace, and dredging to put retrace spells in your graveyard.
Scouting Trek is excellent late-game, as it fetches all your lands, and grants you a retrace spell every turn. (Worm Harvest)
Creakwood Liege adds a nice game-finisher, especially with Worm Harvest (once again).
Groundskeeper is a definite must in this deck.
Cartographer can also bring back lands, although not as well as groundskeepers or life from the loam.
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