Activate Lurking Roper using Overgrown Arch's first ability by tapping it, causing you to gain 1 life.
Lurking Roper triggers, untapping itself.
Repeat.

Infinite lifegain

Infinite lifegain triggers

Agatha's Soul Cauldron

Lurking Roper

Overgrown Arch

Activate Famished Paladin using Overgrown Arch's first ability by tapping it, causing you to gain 1 life.
Famished Paladin triggers, untapping itself.
Repeat.

Famished Paladin

Activate Overgrown Arch by tapping it, causing you to gain life.
The Destined White Mage triggers, putting a +1/+1 counter on Crystalline Crawler.
Activate Crystalline Crawler ability by removing a +1/+1 counter from it, adding {U}.
Activate Pemmin's Aura's ability by paying {U}, untapping Overgrown Arch.
Repeat.

Combos with "Overgrown Arch"