tame temple
My suggestion for Mario VS Luigi online; four new playable characters, two separate move sets.
The newcomers: Sonic/Shadow & Sora/Roxas
Sonic and Sora would both start out in a smaller state just like Mario and Luigi.
This means that Sonic can't boost, but he can still home attack and spindash.
As for Sora, he doesn't have any magic points in his status but still can do phyical attacks, guard and roll.
Shadow runs slower and has a little less boost gauge than Sonic, but he has a much more accurate homing attack.
As for Roxas, he has 1 less MP than Sora and a slightly bigger hurt box. However, he has longer range attacks in general.
Sonic would still have the ring system as his health and would start off with only 0 rings. Coins would translate to rings for Sonic. Regular mushrooms and enemies are opportunities to fill up your boost gauge.
As for Sora, instead of 1 item slot, he has 3 of them (a completely different HUD menu for that matter). He also has 30 HP and 3 MP (one hit on him translates to 10 HP of damage). Regular mushrooms would restore his HP while coins would restore his MP.
Once they get a regular mushroom, Sonic can now boost while Sora has access to MP moves.
Sonic's boost can bump players but can't damage them in the boost's regular state. Same can be said with his spindash and homing attack.
Sora's phyical attacks will never damage players, but rather bump them instead. Same can be said for the magic abilities unless it's temporarily upgraded via. a powerup. The magic he has for this move set would be Fire, Blizzard and Thunder (costs 0.5 MP perspective).
Powerups:
Sonic/Shadow:
Fire Flower- The boost's hit box is now bigger and will deal damage to the player. However, it dose drain the boost gauge faster than the normal boost when in use.
Blue Shell- Spindash or home attack to activate the powerup's ability (can deal damage durring activation).
Propeller Mushroom- Starts off with a tornado jump that gose off quickly. Any player caught in its winds are bound to get bumped up high. It's more faster and fluent when falling back down to the ground (horizontally).
Ice Flower- Just regular boosting but the boost gauge is now frozen, meaning that you could boost infinitely if you wanted to. However, it could never create ice cubes inside of players.
Sora/Roxas:
Fire Flower- Upgrades Fire to Firaga, giving it a larger hit box and can deal damage (costs 2 MP).
Blue Shell- Roll to activate the powerup's ability.
Propeller Mushroom- Upgrades Thunder to Thundaga; similar to Fire Flower's description. It has a 40% chance of stunning a player before taking damage. Also gives him the ability to fly.
Ice Flower- Upgrades Blizzard to Blizzaga; similar to Fire Flower's description. It could still put players into an ice cube as well but it's a 25% occurrence.
Mini Mushroom, Mega Mushroom and Super Star are left untouched for these move sets.
Sonic's model: https://www.models-resource.com/ds_dsi/sonicrush/model/11250/
Shadow's model: https://www.models-resource.com/ds_dsi/sonicchroniclesthedarkbrotherhood/model/22658/
Sora's model (texture): https://www.textures-resource.com/ds_dsi/kingdomheartsrecoded/texture/10318/
Roxas' model: https://www.models-resource.com/ds_dsi/kingdomhearts3582days/model/44882/
One more thing, Sora/Roxas can grab foes while Sonic/Shadow can't. Neither of them can wall jump.
verbal moat
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scenic scaffold