DNA Donors: Dhelmise / Miltank
Offspring name: Helltank
New Type: Ghost / Normal
Base Stats: 84 / 105 / 120 / 63 / 100 / 70 (+2 HP, +18 Def, +20 SpD)
New ability and desc: Buns of Steel (Steelworker + Thick Fat) - This Pokémon has the resistances of Steel-types. (Not the Poison immunity, though.)
Notable Moves:
: Body Slam, Shadow Claw, Anchor Shot, Earthquake, Knock Off, Seismic Toss, Counter, Rapid Spin
: Milk Drink, Stealth Rock, Thunder Wave, Heal Bell
Role Identification: This is a rather tame variety of defensive fusion, inspired by FE #182 Miltrank. It does what Miltank does, except it has access to a few Dhelmise tools in Rapid Spin, Knock Off, Anchor Shot, and STAB Shadow Claw.
Now let's talk about typing specifics.
2*: Dark
0.5*: Bug, Poison
0*: Fighting, Ghost, Normal
2* via bypassing immunities: Fighting, Ghost
0.5* via Buns of Steel: Dragon, Fairy, Flying, Grass, Ice, Psychic, Rock, Steel
So, under ordinary circumstances, Helltank has 3 immunities and effectively 10 resistances, all with only 1 weakness. (Electric, Fire, Ground, and Water are uninvolved.)