For commander card suggestions! It's essentially just blue tempo control with some cute proliferate synergies but I like it a whole lot more than Talrand.
For Deekah, I'll start with a category of cards I like, though they tend to be up there on the mana curve, so definitely don't play all of them. Cards that let you get two cast triggers in one spell for Deekah, by allowing you to cast another instant or sorcery (and in some cases, get an even bigger Fractal in the deal by freecasting a bigger spell.) You can do that for interaction:
For theft or recursion:
(Sorcerous squall in particular also gets you a 9/9 fractal while only costing only three, and another fractal from the spell you cast.)
Cipher on arcane heist is also pretty great, since every turn you get in damage you get a free cast and free 4/4, and your commander can make things unblockable, and you can cipher it on the very fractal it makes.
As far as lower cost cards, ones that reduce their own cost (significantly in some cases) are of course welcome, especially if the condition is easy to fulfill.
You get the gist!
Illithid Harvester is a personal favorite as far as a sweeper in mono blue, you can use either half or both!
Finally, I will point out this category of cards:
Your fractals are 0/0s that get their power (and toughness) for their counters. If you turn them into copies of another creature, (assuming you have enough), it's the equivalent for them to casting an overrun, all your Fractals become base 3/3s or 4/4s with all their counters still buffing them. Or gain evasion if you have a random flier. And those cards also have other fun uses.
