The reason why Sheltron costs 50 gauge is because it has no recast timer, so you can use it back-to-back unlike DRK WAR GNB can't use TBN, Raw Intuition,Heart of Stone back-to-back. Onslaught has gauge cost because it also has 20' range. If you nerf the range to 15', you can remove its gauge cost, but that 20' makes it as good as Shoulder Tackle/SSD for dashing across the arena.