I have no idea why but Im having trouble on putting up a good moveset for this old guy!
Relicanth (M) Impish Nature Ability: Rock Head Evs: +Atk/+Def/+Hp
Eh from your EVs/Nature it seems your running more of a support Relicanth so do something along the lines of this; Relicanth @ Leftovers Trait: Rock Head Impish Nature EVs: 252 HP / 4 Atk / 252 Def -Toxic -Head Smash -Waterfall -Stealth Rock
An offensive relicanth would probably look like; Relicanth @ Life Orb Trait: Rock Head Adamant Nature EVs: 252 Atk / 4 Def / 252 Spe -Head Smash -Rock Polish -Waterfall -Earthquake
First time move setting, forgive me if I suck. If you want power, here is a choice band set:
RockyChoiceCanth @ Choice Band Nature: Impish Trait: Rock head EVs: 252 Atk, 252 Spd, 4 Def.
Head smash is great for Rock Head and choice band, having great power with stab, Stone edge is for crits if you like to go haxy. Aqua tail is great power, but if you prefer accuracy over power and hax with flinch, then go right ahead, waterfall is their. Earthquake, no explanation. Double edge is just for great power to go with rock head, but if you want coverage against grass, bounce is your friend.
Here is one for going fast:
PolishingShoes @ Life Orb Nature: Impish Trait: Rock head EVs: 252 Atk, 252 Spd, 4 Def.
What boosts speed? Rock polish. This is the main move for the set, as it boosts speed. Use it a few times and most likely you will be speedin'. Head smash, STAB, to go with Rock head. Aqua tail, awesome power, but waterfall can be used for flinches and better accuracy. STAB too. E-quake, again, no explanation.
Hope I helped!