After finally getting through the Diamond 1 slog, I got placed at rank 95, so here's the deck I used to do most of my Diamond climbing:
12-sweeper control with a relic theme! Feels like it has generally decent matchups, as long as you have a ramp card and an answer or two in your opening hand, things should go smoothly. Deck's heavy on Justice to make use of Enter the Monastery, and as a result there's no good access to face aegis currently, so be careful against hand-hate. Abyssal Scrying can do some absolutely absurd things in this deck: sweeper into relic weapon into Abyssal Scrying can be a clean win in many matchups.
Games end generally in two ways: sticking a massive greatsword and proceeding to mash the opponent's face in whilst keeping the board clear with sweepers; or dropping a Pit of Lenekta and pummeling them with worms.
The market's currently filled with a broad variety of answers, and the fact that Great Valley Smuggler is a 4/4 with any relics out makes them a good blocker as well. Lumen Reclaimer is a must-have for when an opponent's playing mill against you, Turn to Seed is great to eat irritating units like Jekk, Helio, etc. Edict of Linrei hits both Yetis and Stonescar aggro, both of which you want as many removal spells as possible against. Omen of Austerity is market hate that also counts as a relic once played, but could easily be swapped out for Disjunction or even a counterspell (because of prideleader in maindeck)
PS: If it's the only thing you can do with your mana, don't be afraid to cast Abyssal Scrying for only 2 cards - waiting to draw a bigger relic is often a mistake, because you need to draw into it, then play said expensive relic, and then the turn after that finally play Scrying.