Ben 10

There are 3 Sumo Slammer cards in each stage, for a total 18 that you need to collect. You can see how many you have in each stage from the level select screen at the campground (at your RV). Here is a list of their locations in each stage:

The City

• Just past where you talk to Zombozo near a Buzzkill Battery and you fight a group of enemies, keep heading to the right and look for a wooden fence with metal scaffolding behind it. Go into the entrance to the right of the fence and the card will be behind the scaffolding in there
• When you get to the area with all the shipping containers, keep heading up along the right hand side and when you get to the end you will see an opening between a red and green container where the card will be hidden
• (Requires you to return once you have Diamondhead) After you drop off the roof section and fight a bunch of enemies, head up the street to a set of crystals in the corner of a building. Use Diamondhead to create a crystal pillar to take you up to the roof of the building on the right where you will find a card

The Funhouse

• After you pass through the door with Grey Matter you will come to a large room. Circle your way around to the left and you will find the card behind some boxes in the bottom left corner area
• Shortly after getting XLR8, you will drop down into a section where there are leaves on the ground. Use Wildvine to get up to the pipes, then look in the background for a hole in the wall filled with wooden boxes in it just below you. Jump there and break the boxes to find the card hidden behind them
• (Requires you to return once you have Diamondhead) After you turn the corner into a larger area and fight a bunch of enemies, keep going to the right along the upper portion of the screen until you find some leaves on a raised section. Use Wildvine to get up to the higher section, then run to the back of that area to find some crystals. Use Diamondhead to create a crystal pillar to get up to the next section and then go all the way to the back of that room to find the card

The Scrapyard

• After you cross the wooden bridge section and get to the solid ground area with the cars and containers, keep heading to your left until you see a stack of boxes blocking a small alcove (next to 3 red stacked barrels). Break the boxes and then use Grey matter to enter the door in the back. In the next area the card will be to your upper right
• After you fight a group of enemies in front of some pipes in the background and a demolition ball machine, keep heading to the right until you see two outhouse like structures. The card will be inside the second one
• Later on in the level when you come down from a higher area and drop down a little you will find a group of leaves that you need Wildvine to use to bring you up to the higher section in front of you. Once up there, head to your left down past the building ther eand look for two stacks of cars in front of an area between the two buildings there. The card is hidden back behind them in that area

The Hive

• After using Diamondhead to get up to an upper area, keep heading to your right until you see a large opening filled with boxes in the back ground. Break through the boxes into that room, then break set of them in there to find the card hidden back there
• After you've been climbing up for a while, you will come to an area with the background wide open showing off the cavern. Keep going to the left across the wooden section and then jump up the rocks at the end to make it up a level. Head into the cave behind you at the top and hand to the left when you enter it to find a card over there between the red barrels
• (Requires you to return once you have Stinkfly) After you have been climbing up for a while, you will come to an area with the background wide open and in the middle lower area of it you will see a platform with the card on it. You must use Stinkfly to float down to it to collect it

The Canyon

• When you need to use Overflow to jump over a canyon at the beginning, when you land on the next ground spot, the card will be right there
• After using Stinkfly to cross a gap, make your way to the lower section of this area to find a Grey Matter door behind some boxes. Go through the door and in the next area, go to the right and up to the higher ground to find the card there by some boxes
• A short distance from the one above, you will fight some enemies and then come to an area where there is path that goes off into the background (there is an upgrade spot to the right of it). Follow that path all the way back and jump to the small pillar at the end to find the card on it

The Tornado

• After riding up a stone platform, head to your left and jump over to the stone area with all the boxes. Behind the boxes at the far left is where the card is hidden
• After a while, you will ride up another stone platform and when you head to the right to the next stone area there will be a some enemies appear that aren't required to kill (no energy barrier). Switch to Stinkfly, then jump off the stone and float down towards the Weatherhead Tower towards the right aiming for a stone spot attached to it with the card on it (Do NOT get this card if you are trying to get Riding The Storm as the only way you can get off the spot where the card is to fall off and be returned to where you were)
• When you are riding up the final stone platform, head to the right side of it and look for a moving stone platform to appear from that side and jump to it. Ride it around to another stone platform and then take out the enemies there. After they are defeated, head to the right to see a small stone island with the card on it

After you collect all 18 of the Sumo Slamma Cards, the trophy will pop.

You can also see a video walkthrough for all their locations HERE (credit to rus199410)