Deadliest Warrior: Legends

This solution is for those attempting the Joke-Weapon achievements POST-PATCH. Myself, and others who have requested this solution from me, were unable to obtain this with the game set on the Easy difficulty setting.
I will cover everything I did in order to get this achievement, and the similar DLC achievement for Joan of Arc's Joke-Weapon:

Using the method I have developed listed in this solution, I was able to do the same for every character's Joke-Weapon on the Deadliest difficulty setting. I know this is a bit of a long read, but I promise, if you want this achievement, it's worth it.

First, for all the characters, you will have to unlock their Joke-Weapons. In order to do this, you will need to defeat a total of 25 warriors in a single go within Survival Slice mode, which is unlocked under Challenges after you have beaten the game with every one of the characters. I suggest doing this on Easy, and knocking out the following achievement on your way to working on this one:
Once you have your Joke-Weapons unlocked, go into the game's settings at the Main Menu and change the difficulty settings to Deadliest. With our Joke-Weapons, were going to make a 'joke' out of this difficulty!!!

The Do's and Dont's:
1) You CAN die and retry as many times as it takes.
2) You CAN lose the Challenges against Mack. For the challenges, if you accidently use the inproper weapon and still lose, you will need to start over. I found this out by accident while going for Shaka Zulu's Joke-Weapon Title.
3) You ARE allowed to Shove and Grapple, but if you do so, you need to make sure that you are doing it with the required weapon for the achievement, otherwise you will void the achievement unlocking.
4) You CAN Block, in fact, you have to.
5) Do NOT ever fire/throw a projectile, I never did, so I don't know if accidentally doing so will void you getting the achievement even if you purposely lose the match after doing so and Retry.
6) You need to defeat your opponent in both the rounds, winning by the time running out does not count, so make sure to kill or ring-out your opponent.
7) For Joan of Arc and other characters with Pole-Arm Joke-Weapons, if you are damaged enough and lose use of one of your arms, you will automatically switch weapons. Be aware of this, and if it happens, just let the computer defeat you and try again next round/match.

When selecting your character Load-outs/Setups, if the joke weapon is Low-Damage, choose the armor that has a higher defense rating. If the joke weapon is Low-Speed, make sure that you select the armor that has the higher Speed rating. I found myself selecting the lighter armor equipment more often for speed purposes, but for joke weapons that have decent speed ratings, armor type is personal preference.

Always go for Grapple-Finishers.
To perform a Grapple-Finisher, you must first connect with a grapple, which is A+X for any character, and then select Y which is the input for the Finisher (or Final Strike). If your opponent doesn't match your Y input, the Finisher will succeed and you will kill them.
If you just go for the Grapple right from the get-go, the AI will always dodge, and you can get punished if you do so. So you need to be strategic in setting up your opponent for a grapple.
At the end of a combo, any player (whether it's an actual person or just the AI) is vulnerable. So what you need to do is when you are near your opponent: keep blocking, let the AI attack you, and wait until you KNOW that your opponent is done with their combo. A few of the combos have a late hit at the end that can be really deceptive and annoying (Shaka Zulu). The instant they are done with the combo, go for a grapple. Only a few times will you need to move closer before going for the grapple; you may need to do so when facing Attila the Hun.

IMPORTANT(1): ALWAYS, I mean ALWAYS, make sure that your Stamina meter is either all the way full, or almost (90%) full before engaging the enemy. This is because when they perform a combo against you, it will bring your Stamina down at least 80%, which is just enough for a single Grapple attempt (Grapple attempts also cost Stamina). Sometimes your enemy may take your Stamina all the way down; just pay attention, and if this happens run away.
If/When you connect with a Grapple, most of the time the AI wont cancel you when you attempt a finisher, so you can get an easy win early in the match (a few times I was actually able to get a Perfect, but that didn't happen often). Some enemies, however, enjoy being cruel and canceling you, but I found that in a single round, if you succeed 3 Grapple attempts, going for the finisher on the 3rd attempt almost always works.

IMPORTANT(2): Never run in a straight line. When you start the match, run at a slight angle/curve towards your enemy. There is nothing like getting instant killed by a projectile headshot at the start of the match. At the end of a baiting attempt, if you don't have any stamina left, run away. Again, run in a "slight" circular motion so that if they launch a projectile, it wont hit you. William Wallace's arrows sometimes will still hit you, so sometimes if you notice an AI firing something, throw a Right-Joystick dodge into your run. This usually isn't necessary and it makes the time to regain your stamina take longer, but if you feel the need to dodge, feel free to. When your Stamina is finally full again, bait the enemy in and let them engage you so you can go for another Grapple attempt.
If they fail a grapple against you, or you fail a grapple against them, never go for a grapple afterwords, it wont work out. The enemy is (usually) not vulnerable after they fail an attempt. When you get Grapple-Canceled, although you are set up in a position to get pwned, your character can react to your controls before your opponent can attack, so immediately run away like I mentioned above.

Once in a blue moon, pushing works in your favor. I found that Vlad and Cortez were the two most succeptable to Ring-Outs, Alexander can give you some problems, and if he has the chance, he will push you out. Shaka Zulu...you can try it, if it works for you, awesome!!!
Sometimes combos can work in your favor in place of a push and will knock your enemy backwards, but I almost always just went for Grapple-Finishers.
More than likely, the hardest person you will find to beat with any character is Shaka Zulu. He always gave me the most trouble, so if you are struggling against him, just be patient, you will get through him eventually.

I would also like to add that while Online Titles do not matter at all achievement-wise, you will unlock titles for beating the game with each of the characters on Deadliest with their Joke-Weapons. Hernan Cortez's is pretty cool, if I remember correctly, the title you get for his is "Reaper".

Let me know if you guys have any questions, find out or clear anything up such as accidentally firing projectiles, or if you have an alternative method/strategy and I'll edit my solution. I hope this helps everyone who reads this.

hey try beating the arcade on easy using the yax combo it gave me the cheevo and if that doesnt work well i guess mine was glitched for a while and finally unlocked

Wanderer's guide is great, I just wanted to share my experience unlocking this achievement on Easy difficulty, post-patch. I removed the title update under the game data from my hard drive and didn't accept the install when I started up the game again. I had already earned the dead fish by killing 25 warriors in survival slice mode with Genghis Khan.

I left my difficulty on Easy, like usual, and started the Arcade mode with Genghis Khan, making sure to choose the dead fish as the close-range weapon. Whenever a match started, I switched to the fish. I only attacked with the fish, and no other weapons. I did, however, use the spear to block a few times when I switched too late. I spammed the YYY and the YAX combos until I had either killed the other warrior or knocked them off the stage.

I won a few rounds using the grapple technique, but for the most part, I stuck with the combos to get the kill. I never let time run out, and if I thought I wasn't going to be able to finish them, I let them kill me. I unlocked the achievement even with having been defeated in both individual rounds and losing matches. I just hit retry and kept trying. I got the Joan of Arc joke weapon achievement having lost a challenge to Mack, so I don't think it matters if you lose those. So, to recap:

-Get at least 25 kills in survival slice mode with Genghis Khan.
-Delete the title update and don't let it re-install.
-Set the difficulty to Easy under the settings.
-Select the dead fish and don't attack with anything else.
-Don't let the timer run out.
-Deaths and retries won't stop you from getting the achievement.
-Losing the challenges with Mack won't stop you from getting the achievement.
-Ring-outs and grapple kills are fine as long as you are holding the dead fish.

Hopefully this helps some people that were a bit confused about it like I was and don't think they can do it on Deadliest difficulty. Send me a message if you have any questions about how I got the achievement to unlock.