does stealth rock have a base power or set damadge (such as spikes first time i think it does like 10% damadge then 18% then 25%) its just the other day my friend sent out a yamega (rock doess 4x damadge) and it took off over half its hp is this because of a set power plus its super effective
Stealth Rock is based on immunity of your Pokemon to Rock moves. 0.25x=3.125% of Max HP 0.5× =6.25% of Max HP 1×=12.5% of Max HP 2×=25% of Max HP 4×=50% of Max HP
Yanmega lost half of its HP because it is 4x weak to Rock.