There is an easier way: Everybody can die!
Edit: I changed the solution a little bit to clarify that there is no need to lose internet connection if the host didn't die during the match. Guest players can just quit to main menu and return with different class.The trick is:
if the host dies, he can disconnect the internet cable before wave 49 ends and the game will choose another player to be the host. Note that it won't work by closing the game or quitting to main menu. Host needs to lose internet connection!
Then he can come back to the match with another class. If other players (not the host) died during the speedrun, they can just quit to main menu and come back with another class. EDIT 1:
- All players need to die (wipe) to make the trick work. Credits to D3LTA, Davis 888 and count023.
- Other comment suggests that if only the host dies
during the process, it's ok to disconnect only him. He needs to remember to change his class while he is returning to the match! Credits to cooorpse.
- The team can quit during the final wave (50 or 25 if it is a horde variant). Credits to Davis 888 and Bastian Reader.
Example - when everybody died:
Note: if Snatcher catchs someone, don't use Team Revive as it will count as one death! Just shoot/kill the Snatcher until he releases the player.
This is how my friends discovery the trick:
Credits to:Yarto Plagacho"Do You Even Lift?" solution who inspired my friends to try to stack both achievementsBigErnM"The Perfect Run" original solution which has helped many others players
I made these two pictures to explain how Lift Speedrun works. You can use it for all three new Horde achievements to avoid more than one spawn area; of course, for "You're the support, son" achievement you will need to use your own weapons because you can't buy anything from the Fabricator.