[FA] + [vertical only WD] describes the Onko (Treacherous Fox), which lacks the horizontal moves of your Mastodon. The Onko comes from Wa Shogi, an ancient 11x11 shogi variant, thought to have been played without drops.
On the 10x10 board, I find a pair of Bishops more valuable than a Rook and a Pawn. A single Mastodon should fit somewhere between those two values.
[FA] + [vertical only WD] describes the Onko (Treacherous Fox), which lacks the horizontal moves of your Mastodon. The Onko comes from Wa Shogi, an ancient 11x11 shogi variant, thought to have been played without drops.
On the 10x10 board, I find a pair of Bishops more valuable than a Rook and a Pawn. A single Mastodon should fit somewhere between those two values.