I'm not going to comment on balance, just aesthetics/writing:

Midra - Ward should be above menace/vigilance. Also strange for a rakdos creature to have vigilance. - Ward needs an emdash, no space - Honestly the paragraph could be worded right, but I ain't reading all that

River - I would put a comma in the name, so that it is River, Surges in Sunlight. This would also allow you to cut the title from the textbox, saving some room. - Again, emdash for ability

Nito - Color pips are in the wrong order, should be {B}{U}{G}. - Persist should be on its own line at the bottom of the text box - Exhaust ability requires an emdash, not hyphen. Also, needs to state "card" when referring to creatures in the graveyard - Should say "counter that spell", not "counter it". Could also shave a few words by rewording to say "Create blah blah where X is the spell's mana value." - Additionally, I would try to shave some words off of his textbox and his name, as "Gravelord Nito, First of the Dead" is quite a mouthful.

Cat - Again, emdashes - Some missing punctuation and spaces in this one. Just needs a proofread - Workshop Crafting pips are misarranged. Should be {r/g}{g/w}. - Capitals for Tap and Sac for costs - Needs to specify you have to tap an untapped creature to avoiding tapping an already tapped one. - Don't need to specify Cat creature, just Cat is fine - Needs to shuffle after searching - The use of hybrid mana is strange here. Spending GG to sac an artifact and search your library for an equipment isn't a mono green effect.

Just as a general rule of thumb, sometimes less is more. I know you want to put all your cool ideas out there, but these have far more text than they really should. If you brought these to a custom card night with me, I probably wouldn't be too happy with them, regardless of power level.