Lurking Roper, Elemental Mastery, and Prosperous Innkeeper

Prerequisites

• Lurking Roper on the battlefield
• Elemental Mastery on the battlefield
• Prosperous Innkeeper on the battlefield
• Lurking Roper does not have summoning sickness
• Elemental Mastery attached to Lurking Roper

Steps

1. Activate Lurking Roper by tapping it, creating four 1/1 Elemental creature tokens
2. When the Elementals enter the battlefield, Prosperous Innkeeper's second ability triggers four times
3. Resolve the first Prosperous Innkeeper trigger, causing you to gain 1 life
4. Lurking Roper triggers, untapping itself
5. Repeat

Results

• Infinite creature tokens with haste
• Infinite ETB
• Infinite lifegain
• Infinite lifegain triggers