Assuming these creatures are on the board alone:
Colossus Scenario
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Play the card
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Starts as a 2/2
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Sees itself for its first ability as a zombie you control upon entering battlefield and gives itself +1/+1
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Gives itself +2/+2 for the trigger of its second ability of a zombie coming into your control
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Ends up being 5/5
Lieutenant Scenario
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Play the card
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Starts as 1/1
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Sees itself for first ability and gives itself +2/+2
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Gives itself +2/+2 for its second ability of a human coming onto the battlefield
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Ends up being 5/5
When reinforcing these creatures, the Colossus gets all bonus effects upon entering battlefield but Lieutenant does not. So 2x Colossus yields a 10/10 creature (assuming no other zombies on board) and 2x Lieutenant yields 8/8 creature (assuming no other humans on board). One of the +2/+2 triggers isn’t happening for Lieutenant.