weaknesses:
fast firing weapons, long range weapons that have an angle on you, people waiting for you turn a corner, predictable in rush mode
some shooters and especially splatlings can just shoot through your rush mode, even if you are facing directly towards them. weapons that have an angle on you and are far enough away to not get hit by the hammer can also fairly easily splat you. if you turn a corner in rush mode, the slow turning speed will allow a weapon with a somewhat good time to kill to have an opportunity to splat you as you turn the corner. also, if you use the rush mode from too far away, every single enemy player will see it and easily avoid you or just splat you before you get anything done.
remember that you can swim with hammer active! this allows you to be far less noticeable, making it more difficult to predict what you are doing with the hammer or that you even have it active at all. this combined with the fast jump swing can catch the enemy team by surprise and get you much more value out of the special. the jump swing does activate the rush mode slower though, so only use it if you are close enough for it to actually hit someone. swimming with the hammer also allows you to exit rush mode to avoid longer range weapons or more easily fight the faster shorter range ones, because it is less predictable. that is a lot harder to do now that the duration got nerfed a while back from 9 -> 7.5 seconds.
strengths:
very fast damage to objects, can move or just entirely wipe enemy players, very good against slower weapons, long range one shot, giant hitbox, can eat bombs and block explosions
ultra stamp deals a ton of damage and quick so using it against objects like bubble, crab tanks, wave breakers (just remember to jump), an enemy with booyah bomb armor, and even the rainmaker shield. remember with the rainmaker shield to jump while in rush mode on it so that you don't take too much damage from the shield. and against crab tank, if you use hammer from too far away we run into the same issue as before with splatlings because the crab will have time to increase its firing speed and splat you while you approach. if you use ultra stamp at a good moment, it can move or entirely splat half of or even the entire enemy team. coming at them at an unexpected angle, or just incredibly quickly before you pop the special, they will be taken off guard and will need to quickly adapt. if a charger or splatling has no charge when you approach, or the enemy player doesn't expect you, the only thing they can do is run away or get stamped. it is especially difficult to run away from your rush mode if the enemy has a slow painting weapon or doesn't have a lot of paint around them, or both. if you can get behind enemy lines you can actually chase them into your ink or even your teammates. and if you don't get anyone with the rush mode or even the jump swing, you can actually throw the hammer at people, the same way you throw a sub weapon. this is good for getting someone who did successfully run away or dealing with the enemy backline. this does end your special, but you can still use it right before the special timer runs out which means you can use the special normally and finish it with the hammer throw. and finally, bombs will not be affective against you if you hit them with the hammer, which is especially easy to do. you can also block 1 shot fires pretty easily, like explosions. i have hammered straight through a reefslider explosion before and the entire enemy team was so shocked that we team wiped them.
final notes:
i know this is a lot but i wanted to provide as much as i could to help you out with using the special. now with (hopefully, if this all is actually helpful) better idea of what this special is good at and what can easily knock it down, you can go into games and learn how to use it more effectively. i would recommend going into your games with the specific goal to make your ultra stamp usages get their value, instead of worrying about winning or losing the game. when you are trying to win, you have a lot of things in the game to think about, but if you focus specifically on using the special you will have a lot easier of a time learning how to use it.
hopefully this was helpful, but if you do still have specific things to ask about what i have said i am fine with answering, i might have even forgotten some things that would be useful to know.
