When Darksteel Splicer dies, Nim Deathmantle triggers, causing you to pay ({4} magic symbol) to return Darksteel Splicer from your graveyard to the battlefield, and attach Nim Deathmantle to it.
When Darksteel Splicer enters the battlefield, it triggers, creating at least one 3/3 Phyrexian Golem artifact creature token.
Activate Phyrexian Altar three times by sacrificing three Phyrexian Golems, adding ({3} magic symbol) .
Repeat.
If you have four or more opponents, this combo nets infinite creature tokens and colored mana.