Please take this as positive, constructive critism, but I have noticed a trend of your card ideas are essentially those from MtG. That's not to say drawing inspiration from MtG, or other CCGs, is bad, only in that there is an unwritten rule that new Element cards should be as unique as possible and not a carbon copy of other card games. There are a lot of mechanics in MtG that won't fit here, whether they are due to conflicting game themes or way too OP to slide into Elements. Also, some sort of card image/art is really helpful for people to get a more visual understanding of what you are trying to convey.
As for the card stated above, the unupped version could "borrow" the opponent's creature for 1 turn and the upped could borrow for 2 turns. Otherwise, IMO, the card as stated would be too OP, especially for the cost.