Spelunky

You can solo this Achievement with out any help. Also, the game is actually easier playing it multi-player than solo. Watch below to find out how.

This is a compliment to the other guide, as general hints to unlock this achievement. This is from personal experience in unlocking this achievement, but I hope it's still useful.

You can get lots of health thanks to sacrificing partners, damsels and monsters to Kali and getting the Kapala. In my run, I ended up with 14 health and my "partner" with 4 health when I unlocked this achievement. Sadly some Fire Frog blew up next to a shop by getting hit by a Tiki Trap in the Black Market, so the Shopkeepers were chasing me around. But it was still a successful run and I was able to unlock it. :3

There is also opportunities where you are lucky to find a Jetpack inside the environments thanks to the Udjat Eye, so use sticky bombs to bring it out of there (example in the Jungle). One example is the Alien Lord hiding behind some Forcefield laser traps in the Ice Caves area, because there will be occasions where either the monster or the walls will drop a Jetpack for you as well. ^u^

Also I dunno if it has been mentioned before, but if your partner carries a key (for the chest with the Udjat Eye inside), a Damsel, a weapon or anything else you feel it's important, you can then carry your partner with you and it will hold the item or person, which is very useful to reach your goal quicker and not having them wait at a high area too long. But if you want your main account to have the extra health at the goal, the partner has to drop the Damsel, then you pick them up and you go to the next level from there.

Against Olmec, for safety reasons, I decided to use bombs to blow a path down to the lava, then lure him down and he kills himself with a drop. Make sure that Olmec is on either sides of the room, out of reach, so he doesn't spot you. Then you can safely create a path down to the lava. That way both you and your partner will stay alive. If you have the Jetpack or enough ropes, make sure you climb up the top area of the Olmec room and you can collect more bombs from boxes that way.

NOT A SOLUTION - GENERAL STRATEGY

* Work together! I don't just mean that in the general sense, either! Throw your friends somewhere they couldn't get to alone, carry things for each other, distract enemies while someone else kills them, carry your friends around while they go use the toilet!

* Sacrifice your friends! Shrines to Kali aren't picky about their blood rites, toss your friend up on that shrine if you're short a damsel!

* If you die, don't give up! You can revive each other through the use of coffins located throughout the levels randomly, appearing starting only when a player is dead and in ghost-form.

* Ghosts aren't useless! By pressing X, or your whip button, a ghost can shoot out a puff of air, which is not as harmless as it might sound! Puff loot off of high ledges, stun enemies, stun your friends, push back ghosts, set of traps, or even knock an enemy into your coffin to set yourself free! They can even help light the way in darker levels!

PLEASE NOTE YOU DO NOT HAVE INFINITE LIVES.
At one point, your coffins will stop reviving your friends and instead spawn one of the helper-slaves you can purchase from the shopkeeper.
Personally I've made a lot of progress having second player dead the entire game, using the ghost to light the way, set off traps/enemies, push objects off ledges for me, etc. , saving revives for late in the Temple.

IF YOU'RE GOING IT SOLO, BE AWARE YOU CAN PICK UP YOUR FRIEND AND CARRY THEM WITH YOU!
Your normal set of 4 bombs and 4 rope is split between the characters playing, as well, so make sure to recover their equipment when/if you kill them!