First I'd like to thank Darkchyle, Raegarin & Spit5ire for helping me with the achievement.
What you'll need:
4 players, all with mics & in party chat and committed to work together.
(Credit to EchIlIon: "Just wanted to add that this achievement is possible with just two people.")
Duration to complete:
Roughly 2+ hrs, depending on teamwork & familiarity with the flow of performing team kills. More time required if you are unable to get 50,000 points at the last level (level 20), see below for details.
Achievement will unlock during the game, once the combined team score reaches or exceeds 50,000 points in a single wave/level (which is usually the last wave/level).
We played on Public match, but the achievement can also be unlocked in Player matches.
Map:
Dead Rock, level requirement 30,000 points.
Player placement tips:
All 4 players spread themselves around the electrical vortex.
Player A up top near the metal platform facing the electrical vortex.
Player B at the pipe area nearest the metal platform near the cliff. (You'll need to crouch or slide under the pipe)
Players C & D spread themselves out near the dinosaur skull.
Tips to score points:
Pair off, Player A with Player C, Player B with Player D.
General idea is for Player A to kick enemies towards Player C so that Player C can leash them into the Vortex (& vice versa for Player B with Player D) - not only will both players earn Individual Points but additional Team Points as well. Communications is vital to make sure your partner is ready to leash and kick in their general direction. If your partner is not ready, kite the enemy by running around, even if you can't maneuver at the highest defense level you'd be able to withstand alot of damage.
You should be getting points for skills like Gotcha, Yoink, Not in Kansas.
Avoid double-leashing for Tug-of-War, it won't score as much points unless it is a bonus Skill Kill target. (Credit to Spit5ire: For additional 100 points, use the Flail gun on the target before starting the team combo)
Don't kick enemies near the edges, because the Vortex might just suck them in and deny you & your partner the chance to leash them. So once the enemy is attacking you, check with your partner if their ready, warn them you're about to kick, move back abit from the edge to pull the enemy towards you & kick. Your partner should be able to see the blue-halo outline of the enemy and leash them.
For Player B (see player placement guide above), because of the lack of space, kick your targets along the path instead of towards the Vortex. Your partner (Player D) should still have enough reach to leash your targets.
The goal is to score as much Team points and to complete the level requirements early for additional bonus points! We scored an additional 1.7K points by reaching 30K points with about 27 enemies to spare.
For snipers & fast enemies, just slide towards them & let your team mates leash them. You can also slide under the pipe area for Player B.
If a boss enemy appears, best to ignore the normal enemies and try to help your friends take out bosses. Working together you can also score Team Points like Whiplash or Bossed which are both an additional 300 points each! Boss enemies can be tricky at higher levels, so co-ordinate your attacks carefully. Damaging or killing Boss enemies can cause area damage and kill normal enemies (like the Cannoneer's exploding backpack) so watch out that taking out Boss enemies doesn't deny your team of potential Team points from normal enemies.
For enemies that reward points for skill kills, kite them to the location and kill them together with your team mates.
Skill & weapon management:
1. Upgrade leash, defense & speed (roughly in that order).
2. Those players with excess points should upgrade to Thumper early on in case enemies with skill challenges like Slamdunk appears (I think we encountered our first Slamdunk around level 10).
3. Concentrate only on upgrading the default gun's speed & ammo. We didn't find other weapon unlocks & upgrades useful, and may kill off normal enemies too early. We didn't bother with Charges for the default gun.
4. If a player finds himself low on purchasing points, swap places with Player A (see player placement guide above). We only did this once to help a buddy who had lower points.
Level 20 tips:
1. If you have 10 enemies left & still have not unlocked the achievement, please check with your individual points & total it. If you still have alot more to go before hitting 50,000 points, just get all players to commit suicide and restart the level. If you don't and end the match, you can't restart the level to score 50K points. We did this once when we had only 7 enemies left and were under 40K.
2. The game will spawn multiple enemy bosses so watch out. Work together to take them out. Be prepared to revive downed team mates, yes it does happen.
3. Credit to CloakedVengance: "One thing to add if you are at 48/49k you can leave 2 or 3 bad guys alive and keep getting downed and then reviving people for an easy 50 points a time, we used this method to get us over the finishing line."
I really hope this help those still struggling to get this achievement, we had plenty of close calls but tons of fun playing this game mode.