From Bulbapedia, the community-driven Pokémon encyclopedia.
The Mudkip/Swampert Build 'n Battle set
Pokémon Build 'n Battle was a series of construction toys manufactured by Mega Bloks in the early 2000s. Each building set contained enough blocks to build one of two Pokémon from the same evolutionary family (but not both at the same time), a strength chart, scoring pieces, and two die.
There were four Build 'n Battle sets available: Pikachu/Pichu, Treecko/Grovyle, Torchic/Combusken and Mudkip/Swampert.
Strength chart for Mudkip/Swampert
To battle their Pokémon, players must first place their "strength pieces" on their "Pokédex plate" according to the chart that came with their Pokémon. Players then roll a die to determine who plays first.
The first player chooses a strength attribute (Speed, Attack, Defense, Building Complexity, Building Quickness) to battle with. Their Pokémon then uses this attribute to battle the other Pokémon's (for example, Attack vs. Attack or Speed vs. Speed). Each player rolls the die and the player with the lower number must remove one of their blocks corresponding to the battled attribute. When all the blocks for one attribute have been removed, the corresponding purple block at the back row of the Pokédex plate is also removed.
When at least one player's purple block has been removed for each attribute, the player with the most remaining purple blocks is the winner and they receive a golden block. If the game is a tie, players roll a die to determine the winner. Players can continue to play and compete to win the most golden blocks.