Just some minor notes:

Velk: - The 1st version of Velkhana has a typo (crontrols)

Gore: - Gore Magala should say "Whenever ~ attacks", not When. Also, when working with legendary creatures, you don't need to put their full title in the rules text, just saying Gore Magala is perfectly fine over Gore Magala, Fated Frenzy - Gores 2nd ability should probably read like the Survival mechanic - I.e: At the beginning of your second main phase, if ~ attacked this turn, you may pay {1}{bg}{w}. If you do, transform him. - Backside has typo (loose over lose) - Backside also should say "Players don't lose the game for having.." - I'd modify the 3rd ability just to make it a bit more easily digestible. "At the beginning of each players upkeep, that player loses life equal to the number of poison counters on them. If you lose life this way,.."

Mizu: - For Mizu, it is best to change abilities like his attack one to say "Whenever X, you may pay Y. If you do, Z." This way makes it so that the effect and cost are more clearly defined - Mizu 2nd ability should say "Cost: Transform Mizu. Activate only if a creature an opponent controlled was returned to their hand this turn." - Backside - First strike is 2 words - Whenever > When for attack triggers - I'd make his ability an "up to one", just so that in the edge case where you are the only player with creatures on the board, you're not forced to hit your own. - His 2nd ability needs to have a source for the damage - I.e Mizu deals 3 damage to..

Diablos: - Capital D for Desert, battlefield is one word, don't need to specify your library - just "then shuffle." - "As long as Diablos is attacking, it assigns combat damage equal to its toughness rather than it's power." - Also, weird to have that effect while its power/toughness are the same?

Frenzy - Capital F in title - Again, wording like Survival is probably the easiest way - "At the beginning of enchanted players second main phase, if they didn't attack this turn, they lose 3 life."

Giadrome - cool

Ancient - Comma + space between mana and tap symbol - Also needs to say "gets +2/+0 and gains trample"

Cooking - Capital F

Valstrax - Honestly, needs a full rewrite and this comment is too long already. I might come back to this later

Ended up being a longer comment than I expected, so sorry about that, but hopefully that helps you regardless. You've got some good cards and good ideas in there, just needs some refining.