Hardened Scales + Champion of Lambholt + Token Generator
Four.

When the two tokens enter the battlefield, Champion of Lambholt's triggered ability triggers twice. It will be placed on the stack twice. When the topmost instance resolves, it would add a +1/+1 counter to Champion of Lambholt. Instead, it adds one extra, so two. When the other instance resolves, it will also add two, so a total of 4 +1/+1 counters are added to Champion of Lambholt.