Grass - Weedicide kills weeds and plants, preventing them from invading gardens
Level Up is the mechanic that Class was based on, and appears on creatures (known as Levelers)
It's strong in ETB heavy brews like midrange and blink, sacrifice brews where you can sacrifice to something like Attrition and then come back, Aristocrats where you can trigger Blood Artist for wins, life gain for lifelink shenanigans, Voltron and equipment that invested in equipment infrastructure to and any heavy creature build
The most impressive one to chase after in the bunch is Shaymin
Whether you're on the side of the wild dragons, the resolute clans, or both, Tarkir: Dragonstorm has plenty of cards for your decks
You are never forced to activate mana abilities to pay costs, so if there is a mandatory additional mana cost (such as from Thalia, Guardian of Thraben), you can decline to activate mana abilities to pay for it and hence fail to cast the suspended card, leaving it in exile