Timeline Culler either from your hand or from your graveyard for its warp cost by paying ({B} magic symbol) and 2 life.
Activate
Phyrexian Altar by sacrificing
Timeline Culler, adding ({B} magic symbol) .
When
Timeline Culler dies,
Proper Burial triggers, causing you to gain 2 life.
Repeat.
Notes
If
Timeline Culler is in your hand, you can instead cast it normally and then cast it via its warp cost on each other iteration. This adds ({B} magic symbol) to the mana needed but removes the life requirement.