Torterra is really slow! Is there a way you can make him faster in Pokemon Diamond? A Magickarp literally strikes before him! I've tried using that speed medicine, but he's still really slow!
There was a really similar question to this I found somewhere. For Torterra you could:
Ev train him 252 Spe to max out his speed
Baton pass it speed boosts from other Pokemon which can learn speed boosting moves or have another Pokemon use tailwind
Teach Torterra speed boosting moves like Rock Polish as sumwun said
Give Torterra things like Choice scarf (boosts speed by 1.5x but only allows you to select one move), Quick Claw (Allows you to move first occasionally), X-Speed (raises speed by 2 stages in battle) and Salac berry (raises speed by 1 stage when at 25% health and below)
(Note: Torterra itself will always be slow most of the time even with the above methods so it’s better to do what Sumwun suggested and make it bulky with reliable recovery instead) Hope this helps!
Edit: forgot this was gen 4 removed Ivs and natures
The other answers haven't mentioned this, but you can level grind your Torterra. This is much easier than messing with EVs, natures, or IVs, carrying around a Pokemon that learns baton pass but is otherwise useless, or getting a choice scarf, and it's much more reliable than a quick claw. It also raises Torterra's damage and all of Torterra's other stats. If you don't want to use your rock polish TM, this is the easiest way to do it.
Rock Polish, Jolly nature, 252 Speed EV's and a Choice Scarf will help nicely. In Gen IX Turtwig gets Shell Smash, which is better than Rock Polish. Good luck.
