Word Search II: Trie Approach

Build a trie containing all target words. Then DFS from each cell:

function findWords(board, words):
    trie = buildTrie(words)
    result = []

    function dfs(r, c, node, path):
        if node.word:
            result.append(node.word)
            node.word = null // avoid duplicates
        if r < 0 or r >= rows or c < 0 or c >= cols:
            return
        char = board[r][c]
        if char not in node.children:
            return
        board[r][c] = '#' // mark visited
        for dr, dc in [(0,1),(0,-1),(1,0),(-1,0)]:
            dfs(r+dr, c+dc, node.children[char], path+char)
        board[r][c] = char // restore

    for r from 0 to rows - 1:
        for c from 0 to cols - 1:
            dfs(r, c, trie.root, "")
    return result

The trie prunes search paths early. If the current path isn't a prefix of any target word, you stop immediately.