You control at least nine other nontoken creatures.
This pre-requisite can be reduced if you control one or more nontoken Angels with toughness 2+, or if you have creature cards in your graveyard plus additional ({WB} magic symbol) mana and/or Blood tokens.
Steps
Activate
Shilgengar's first ability by sacrificing another nontoken creature, creating at least one Blood artifact token.
Repeat step 1 until you control at least six Blood tokens.
Activate
Phyrexian Altar by sacrificing another nontoken creature, adding ({WB} magic symbol) .
Repeat step 3 until you have ({WB} magic symbol) ({WB} magic symbol) ({WB} magic symbol) available.
Activate
Shilgengar by paying ({WB} magic symbol) ({WB} magic symbol) ({WB} magic symbol) and sacrificing six Blood tokens, returning all creature cards from your graveyard to the battlefield without a finality counter on them due to
Solemnity.
Repeat.
If you control additional nontoken creatures, you may sacrifice them in step 1 to get infinite Blood tokens, and/or in step 3 to get infinite colored mana.