If the gift was promised and the target is illegal as Valley Rally tries to resolve, it won't resolve and none of its effects will happen
However, instead of being able to add counters itself, Omarthis gets additional counters whenever you put more plus-one plus-one counters on other permanents
Another notable green card is Augur of Autumn , a Human Druid that can look at the library's top card and play lands from there, just like Courser of Kruphix
Using any of these tools requires branching out into two or three colors, but that shouldnt be too much of a problem
But even if they dont, you can activate its ability to force them to draw a card after their initial one so you get another card as well
Accordingly, it is not possible to dull the same Backup card to generate the CP required to pay the cost for Mateus the Corrupt