Rielle is a powerful brawl commander that isn't often seen in the matchmaking. While she lacks ETB/on cast effects or death triggers, her low mana cost, combined with high quantity of cheap instant speed discard options for UR makes it possible to secure some value with her nontheless. 

The priority of this build is not just to synergize with Rielle's triggered ability, but also to have enough interactions to interdict most opposing strategies, hence the ample control and removal cards. Luckily, we retain enough discard outlets to get the Rielle engine going. And the more you draw, the more discard options you will find.

After ~100 games and several revisions, here are some of the best performing cards that synergize with Rielle's ability:

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And of course, Flame of Anor, which is obscenely strong with wizards in general.

I recommend playing these cards with Rielle, regardless of whether you are leaning more into control or combo. A onesided boardwipe with Nahiri's Wrath or doubling your hand with a Channeled Force is what makes this deck so incredibly fun. Most of them are also great cards on their own, which is essential when our commander is so frail. 

You could adjust the counter spells and removes to your liking, above are my personal favorites over hundreds of UR control games.

To close the game, assuming opponent refuses to tap out, my chosen finishers are The Royal Scions, which can give a high power Rielle the terrifying combo of first strike and trample while working towards a potent -8 with Rielle's drawing power; Gandalf's Sanction, which can often deal 20 damage upstairs out of the blue (and the red); Wizard Class, whose level 3 can grow the flyers to epic proportion. Meanwhile we still have the classic wincons like Niv, Shark and Explosion at our disposal. 

Finally, here are some strategic advices. Try not to rush out Rielle against black, monoR and open blue mana, this deck is well suited to play draw-go if opponent refuses to commit first, it's more important to control the tempo. Try not to be too timid either, Rielle + Faithless Looting will immediately give you 2 extra cards, which is already decent value even if she is removed later. Several of our spells, including Rielle herself, scale with the graveyard, so be wary of graveyard hate if you can afford to.