Attack with Spiteful Sliver.
When Spiteful Sliver deals damage, Guilty Conscience triggers, dealing damage to Spiteful Sliver equal to the amount of damage Spiteful Sliver dealt.
Spiteful Sliver triggers, dealing damage equal to the amount of damage Guilty Conscience dealt to it to target player or planeswalker.
Repeat from step 2.

Infinite damage

Guilty Conscience

Spiteful Sliver

Indestructibility

Deal damage to Spiteful Sliver.
Spiteful Sliver triggers, dealing that much damage to target player or planeswalker.
Guilty Conscience triggers, dealing that much damage to Spiteful Sliver.
Repeat.

Combos with "Spiteful Sliver"