Pay two mana and tap Dina to sacrifice another a creature and you'll gain X life and put X +1/+1 counters on another target creature. X is the sacrificed creature’s power.
The idea is obvious, then: Sacrifice a big-hitter to power up another card and gain a bunch of life. And the hitters don’t come much bigger than Jumbo Cactuar.
This rare creature from the Final Fantasy set is a 1/7 plant that has the ability 10,000 Needles: Whenever it attacks, it gets +9999/+0 until the end of the turn. (And no, that’s not a typo.)
If you can get both Jumbo Cactuar and Dina onto the battlefield — and wait for them to overcome summoning sickness — it's a serious problem. Declare Jumbo Cactuar as an attacker and then activate Dina’s ability to gain 10,000 life and place 10,000 +1/+1 counters on a creature. For all intents and purposes, it’s going to end the game.
The only real mitigation here is that while Dina is only a three-cost card, Jumbo Cactuar will set you back seven mana. Then again, if there's one thing green is good at doing in Magic, it's helping you ramp up to extra mana early in the game.