Yuna, Grand Summoner + Ioreth of the Healing House + Saryth, the Viper's Fang

Yuna, Grand Summoner

Ioreth of the Healing House

Saryth, the Viper's Fang

How it works

1. Activate Yuna by tapping it, adding 1 and causing the next creature spell you cast to enter with two +1/+1 counters on it.
2. Activate Saryth by paying 1 and tapping it, untapping Ioreth.
3. Activate Ioreth's second ability by tapping it, untapping Saryth and Yuna.
4. Repeat an arbitrarily large number of times.
5. Cast a creature spell, causing it to enter the battlefield with infinite +1/+1 counters due to Yuna.