Gain 3-5 scrap this turn only (costs 3 or less mana, probably 2)
This turn only? I like that!
Destroy all bots, players gain their scrap value
This reminds me about Day of Judgement in MTG, and there's some related HS cards as well for it. I like that they are automatically scrapped. This is a powerful card if you have more cards than your opponent on hand and should probably have quite high casting cost.
Destroy one Bio unit immediately
Powerful. Perhaps a bit too powerful. At least given how the current attack system works.
Remove all buffs/enchantments from one Bio
Removing *all* might be a bit excessive. But removing one or two enchantments might be reasonable. Although again, how the current attack system works this might be very powerful.
Opponent cannot scrap cards next turn
This one I *really* like. This can lead to some different strategies. I like the thought of preventing opponent from doing something.
Opponent loses all scrap
Aaaw. Poor opponent. I think he'll survive. Sounds like a reasonable effect. Then you'd be more careful with scrapping, probably. I just hope this isn't too powerful.
Steal X scrap from opponent
Stealing scrap? Sure, why not? X should probably be quite low though.
Opponent cannot play Bio units next turn
Again, I like the thought of preventing opponent from doing something.
Deal X damage to all Bots
I think this better than destroying all creatures. Especially if this damage can be combined with actual attacking to destroy "creatures".
Your Bots gain X attack this turn only.
X should probably be quite low.
Your Bots gain X health next turn
Seems useful for a defensive strategy
Buff a Bio unit X/X for a cost in mana (no scrap cost)
Hmm. I am not sure about this. Perhaps if it is "this turn only"
Buff a Bot by X/X costing all of your scrap
What if I only have one scrap? Should the X be dependent on my scrap or something? If it is, then I think it can work. Should perhaps be "this turn only".
The next enchant you play this turn costs 0 scrap
I like the card, but I would probably not play it myself. But I think that it is a good card to add to get some players to think "Hmm, this I could combine together with that to make a super über combo".
Opponent cannot play enchantments next turn
Oh how I would love to have had this card when I played you recently!
I'd also like to see...
Cards with various bonuses / drawbacks such as: (some more or less crazy examples)
1/4 B0T for 3 mana: At the beginning of your turn, draw an extra card
4/4 Bio for 3 mana: You may only play one card per turn.
2/2 Enchantment for 2 scrap: Enchanted creature can only attack each 2nd turn.
3/3 Bio for 3 mana: Your enchantments costs twice as much scrap.
5/5 B0T for 3 mana: All your creatures have maximum 5 attack
0/7 Bio for 6 mana: Your opponent can only attack with one creature each turn
These bonuses and drawbacks can of course be made in several different variations to find out what works best.
Note that you don't need to worry about how these cards should be implemented. I assure you, they will be able to be implemented.