You control a nontoken creature with greater mana value than Stickytongue Sentinel that can be cast using only mana creatures you control can produce.

Activate any number of creatures you control by tapping them, adding at least enough mana to cast Stickytongue Sentinel.
Cast Stickytongue Sentinel by paying its mana cost.
When Stickytongue Sentinel enters the battlefield, it, Clement and Intruder Alarm trigger.
Resolve the Clement trigger, returning nothing to your hand.
Resolve the Stickytongue Sentinel trigger, returning the other creature with greater mana value from the battlefield to your hand.
Resolve the Intruder Alarm trigger, untapping all creatures.
Activate any number of creatures you control by tapping them, adding at least enough mana to cast the creature returned to your hand.
Cast the creature by paying its mana cost.
When the creature enters the battlefield, Clement and Intruder Alarm trigger.
Resolve the Clement trigger, returning Stickytongue Sentinel from the battlefield to your hand.
Resolve the Intruder Alarm trigger, untapping all creatures.
Repeat.

You can tap Frogs for mana thanks to Clement. This should be factored in when determining if you have enough mana to execute the combo.

Cast Nethroi either from your hand or from the command zone for its mutate cost by paying , putting it under a non-Human creature you control.
Nethroi triggers, returning Stickytongue Sentinel and Mitotic Slime from your graveyard to the battlefield.
When Stickytongue Sentinel enters, it triggers, returning Nethroi from the battlefield to your hand.
Activate Phyrexian Altar twice by sacrificing Stickytongue Sentinel and Mitotic Slime, adding .
When Mitotic Slime dies, it triggers, creating two 2/2 Ooze creature tokens.
Activate Phyrexian Altar twice by sacrificing the Oozes, adding .
When the Oozes die, they trigger, creating four 1/1 Ooze creature tokens.
Activate Phyrexian Altar three times by sacrificing three Oozes, adding .
Repeat.

During step 2, you can recur other creatures with suitable powers. This will allow you to forego sacrificing that many Oozes in step 8, netting infinite mana and creature tokens. If you have infinite mana and Oozes, you can then forego reanimating Mitotic Slime and reanimate anything else with a suitable power instead.