Enter a 1v1 death match, you as Cutter and opponent as Forge. Send your first warthog to the back of the opponents base and repeatedly spawn them and attack with the Warthogs (only spawn 9). He will try to build a barracks and a vehicle depot, but just destroy them as soon as they come up. You should also get the Big Al's Scooter achievement also as it is obvious that you get this in under 10 minutes.
Enter a 1v1 death match as the Prophet and the opponent as any leader on Blood Gulch. At the start of the match, quickly create a Temple and send your Ghost towards the enemy base as a distraction. Once the Temple is created and Regret is on the field, send him towards the enemy base and use his cleansing beam to destroy the enemy base and/or any enemy units that pose a threat to him. If done efficiently, you should be rewarded with the 'Big Al's Scooter' achievement as well.
Enter a 1v1 regular skirmish game (Heroic) on Chasms, the player as the Brute Chieftain or Prophet of Regret (all you need is a very basic leader rush strategy) and the enemy as Captain Cutter or Sergeant Forge. Build a temple first and then a supply pad, scout for crates and then send the leader (as soon as possible) to the enemies base to start harassing new structures being built. Set your bases waypoint to the teleporter so new special infantry units teleport to the leader upon being trained, use all remaining starting resources to queue up brutes or elite honor guard then build another supply pad and continue training more of these units until you reach the limit of 10 squads (including your leader and ghost or brute chopper). Using brutes or elite honor guard you can destroy the enemy base, done correctly both this achievement and Big Al's Scooter can be unlocked simultaneously.