Spell — Summon • Cost: 3
Sacrifice a green unit. If you do, put a green unit one tech higher that costs 5 or less from your codex into play.
You can't teach an old dog new tricks. Nature's solution: new dogs.
Green • Balance Magic
"One tech higher" means that if you sacrifice a tech 0 unit, you can get a tech I unit. If you sacrifice a tech I unit, you can get a tech II unit. If you sacrifice a tech II unit, you could get a tech III unit, except actually non green tech III units exist that cost 5 or less. — Sirlin, 03/04/16
"Cost 5 or less" refers to the printed gold cost in the upper left corner of the card. Abilities that reduce costs, such as Gigadons, aren't taken into account, so you can never get Gigadon with Circle of Life. — Sirlin, 03/04/16